[PATCH 0/2] smi_detector: a simple module for detecting System Management Interrupts

[PATCH 0/2] smi_detector: a simple module for detecting System Management Interrupts

[Jon Masters]

Folks,

Please take a look at this simple SMI detector that we have written for use
by those who would like to track down excessive duration or otherwise
undesirable System Management Interrupt overhead on their systems.

This is also available as a git branch. To track that:

git pull git://git.kernel.org/pub/scm/linux/kernel/git/jcm/linux-2.6-jcm.git smi_detector

Thanks,

Jon.

[PATCH 1/2] SMI Detector: a simple module for detecting System Management Interrupts

[Jon Masters]

System Management Interrupts (SMIs) are a feature of modern x86-compatible
microprocessors. They allow BIOS provided management code to "borrow" the
system CPU in order to perform certain activities - device emulation,
thermal throttling, fan control, and similar. The CPU exposes the SMI
functionality through a dedicated pin and special purpose logic. When an
SMI is asserted, the CPU suspends the overlying running Operating System
and executes special SMI management routines within a unique context.

SMI routines are usually provided by the system BIOS, and the SMI assertion
is usually made by logic in the system's South Bridge. The Operating System
is typically completely unaware of the presence of an SMI, much less the
amount of time spent handling them. Therein lies the problem. Some of these
SMI routines can take many milliseconds to complete (or even longer,
depending upon the implementation of the routines). Although it is possible
to disable SMIs (typically by poking at the South Bridge LPC or similar),
that can be *EXTREMELY DANGEROUS* because it can result in a system
overheating, or even worse. Therefore, we simply try to detect them. We do
not attempt to disable them and discourage other efforts at doing so. We
instead prefer to collate data and ask BIOS vendors to fix their code.

We have been increasingly concerned about the amount of time certain systems
spend inside System Management Interrupt (SMI) routines, especially on those
systems intended for "real time" applications. This module can be used to
detect SMIs as they occur by periodically grabbing the CPU(s) within a
stop_machine context, and sitting in a tight loop reading the timestamp
counter during the monitoring phase. If we experience unexplained
discontiguous readings in the CPU timestamps, we are able to assert the
presence of an SMI condition (the CPU is doing nothing else at the time).

Since we steal the CPU for relatively long periods of time, this module is
intended primarily for diagnostic use. It should not be used in a normal
production environment unless "enable" is set to zero or the acquisition
parameters are set sufficiently low to avoid performance impact.

There are a number of pending feature improvements to this code but we
would like to get it out there and in use tracking down SMIs.

Signed-off-by: Jon Masters <jcm@jonmasters.org>
---
 Documentation/smi_detector.txt |   94 +++++++++++
 drivers/misc/Kconfig           |   14 ++
 drivers/misc/Makefile          |    1 +
 drivers/misc/smi_detector.c    |  360 ++++++++++++++++++++++++++++++++++++++++
 scripts/smidetect              |  282 +++++++++++++++++++++++++++++++
 5 files changed, 751 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/smi_detector.txt
 create mode 100644 drivers/misc/smi_detector.c
 create mode 100644 scripts/smidetect

diff --git a/Documentation/smi_detector.txt b/Documentation/smi_detector.txt
new file mode 100644
index 0000000..902ff36
--- /dev/null
+++ b/Documentation/smi_detector.txt
@@ -0,0 +1,94 @@
+Introduction:
+-------------
+
+The module smi_detector is a special purpose kernel module that is
+used to detect if System Management Interrupts (SMIs) are causing event
+latencies in the Linux RT kernel.
+
+SMIs are usually not serviced by the Linux kernel. They are set up by
+BIOS code and are serviced by BIOS code, usually for critical events
+such as management of thermal sensors and fans. Sometimes though, SMIs
+are used for other tasks and those tasks can spend an inordinate
+amount of time in the handler (sometimes measured in milliseconds).
+Obviously if you are trying to keep event service latencies down in the
+microsecond range, this is a problem.
+
+The SMI detector works by hogging the cpu for configurable amounts of
+time (by calling stop_machine()), polling the Time Stamp Counter (TSC)
+register for some period, then looking for gaps in the TSC data. Any
+gap indicates a time when the polling was interrupted and since the
+machine is stopped and interrupts turned off the only thing that could
+do that would be an SMI.
+
+Note that the SMI detector should *NEVER* be used in a production
+environment. It is intended to be run manually to determine if the
+hardware platform has a problem with long SMI service routines.
+
+Usage:
+------
+
+Loading the module smi_detector passing the parameter "enabled=1" is the only
+step required to start the smi_detector. It is possible to define a threshold
+in microseconds (us) above which latency spikes will be taken in account
+(parameter "threshold=").
+
+Example:
+
+	# insmod ./smi_detector.ko enabled=1 threshold=100
+
+After the module is loaded, it creates a directory named "smi_detector" under
+the debugfs mountpoint, "/debugfs/smi_detector" for this text. It is necessary
+to have debugfs mounted.
+
+avg_smi_interval_us	- average interval (usecs) between SMI latency spikes
+latency_threshold_us	- minimum latency value to be considered (usecs)
+max_sample_us		- maximum SMI latency spike observed (usecs)
+ms_between_samples	- interval between samples (ms)
+ms_per_sample		- sampling time (ms)
+sample_us		- last sample (usecs). Continously updated, may be used
+			  to plot graphs or to create histograms
+smi_count		- how many latency spikes have been observed
+
+
+	# cd /debugfs/smi_detector
+
+	# cat *
+	0		(avg_smi_interval_us)
+	100		(latency_threshold_us)
+	0		(latency_threshold_us)
+	5000		(ms_between_samples)
+	1		(ms_per_sample)
+	3		(sample_us)
+	0		(smi_count)
+
+
+The default values for ms_between_samples and ms_per_sample define that every
+5000ms (5s) samples will be collected during 1ms. It is possible to change the
+sampling time or the sampling interval writing to the related files. To collect
+samples during 5ms every 50ms:
+
+	# echo 5 > ms_per_sample
+	# echo 50 > ms_between_samples
+
+
+	# cat ms_between_samples
+	50
+	# cat ms_per_sample
+	5
+
+After a while, data may be verified to atest the existence of SMI induced
+latencies:
+
+	# cat smi_count
+	2
+	# cat max_sample_us
+	468
+	# cat avg_smi_interval_us
+	1356306050
+
+Depending on the latencies observed it is important to better adjust the
+sampling intervals to obtain more accurate measurements. Care must be taken
+to not create a continous sampling situation, that might be perceived by the
+kernel as a deadlock.
+
+
diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 1c48408..573ae2e 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -76,6 +76,20 @@ config IBM_ASM
 	  information on the specific driver level and support statement
 	  for your IBM server.
 
+config SMI_DETECTOR
+	tristate "Test module for detecting time gaps caused by SMIs"
+	default m
+	---help---
+	  A simple SMI detector. Use this module to detect large system
+	  latencies introduced by the presence of vendor BIOS SMI
+	  (System Management Interrupts) somehow gone awry. We do this
+	  by hogging all of the CPU(s) for configurable time intervals,
+	  looking to see if something stole time from us. Therefore,
+	  obviously, you should NEVER use this module in a production
+	  environment.
+
+	  If unsure, say N
+
 config PHANTOM
 	tristate "Sensable PHANToM (PCI)"
 	depends on PCI
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index bc11998..7f23e02 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -20,3 +20,4 @@ obj-$(CONFIG_SGI_GRU)		+= sgi-gru/
 obj-$(CONFIG_HP_ILO)		+= hpilo.o
 obj-$(CONFIG_C2PORT)		+= c2port/
 obj-y				+= eeprom/
+obj-$(CONFIG_SMI_DETECTOR)	+= smi_detector.o
diff --git a/drivers/misc/smi_detector.c b/drivers/misc/smi_detector.c
new file mode 100644
index 0000000..40913fc
--- /dev/null
+++ b/drivers/misc/smi_detector.c
@@ -0,0 +1,360 @@
+/*
+ * A simple SMI detector. Use this module to detect large system latencies
+ * introduced by the presence of vendor BIOS SMI (System Management Interrupts)
+ * somehow gone awry. We do this by hogging all of the CPU(s) for configurable
+ * time intervals, looking to see if something stole time from us. Therefore,
+ * obviously, you should NEVER use this module in a production environment.
+ *
+ * Copyright (C) 2008 Jon Masters, Red Hat, Inc. <jcm@redhat.com>
+ *
+ * Miscelleaneous tweaks:  Clark Williams <williams@redhat.com>
+ *
+ * Licensed under the GNU General Public License, version 2.0.
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+
+#include <linux/stop_machine.h>
+#include <linux/time.h>
+#include <linux/hrtimer.h>
+#include <linux/kthread.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+#include <linux/uaccess.h>
+#include <linux/version.h>
+
+/*
+ * The below version code is the code of the git commit where
+ * stop_machine replaced stop_machine_run
+ */
+/*#if LINUX_VERSION_CODE < 132637*/
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 28)
+#define stop_machine  stop_machine_run
+#endif
+
+#define smi_version "0.3.0"
+#define SMI_BANNER "SMI Detector: "
+#define DEFAULT_MS_PER_SAMPLE 1    /* milliseconds */
+#define DEFAULT_MS_SEP_SAMPLE 50   /* milliseconds */
+#define DEFAULT_SMI_THRESHOLD 10   /* microseconds */
+
+MODULE_AUTHOR("Jon Masters <jcm@redhat.com>");
+MODULE_DESCRIPTION("A simple SMI detector");
+MODULE_LICENSE("GPL");
+
+static int debug;
+static int enabled;
+static int threshold;
+
+module_param(debug, int, 0);
+module_param(enabled, int, 0);
+module_param(threshold, int, 0);
+
+DEFINE_MUTEX(enable_mutex);
+
+struct task_struct *smi_kthread;
+
+struct smdata_struct {
+
+	u64	last_sample;
+	u64	max_sample;
+	u64	smi_count;
+	u64	threshold;
+	ktime_t last_spike;
+	u64	frequency;
+
+	atomic_t pending;
+	wait_queue_head_t wq;
+
+} smdata;
+
+static void smi_init_stats(void)
+{
+	smdata.last_sample = 0;
+	smdata.max_sample = 0;
+	smdata.smi_count = 0;
+	smdata.frequency = 0;
+	smdata.threshold = threshold ? threshold : DEFAULT_SMI_THRESHOLD;
+}
+
+
+struct dentry *smi_debug_dir;		/* SMI debugfs directory */
+struct dentry *smi_debug_max;		/* maximum TSC delta */
+struct dentry *smi_debug_smi;		/* SMI detect count */
+struct dentry *smi_debug_sample_ms;	/* sample size ms */
+struct dentry *smi_debug_interval_ms;	/* interval size ms */
+struct dentry *smi_debug_sample;	/* raw SMI samples (us) */
+struct dentry *smi_debug_threshold;	/* latency threshold (us) */
+struct dentry *smi_debug_frequency_us;	/* avg smi spike interval (us) */
+struct dentry *smi_debug_enable;	/* enable/disable smi detection */
+
+u32 smi_sample_ms   = DEFAULT_MS_PER_SAMPLE;    /* sample size ms */
+u32 smi_interval_ms = DEFAULT_MS_SEP_SAMPLE;    /* interval size ms */
+
+/*
+ * smi_get_sample -	Used to repeatedly capture the CPU TSC (or similar),
+ *                      looking for potential SMIs. Called under stop_machine.
+ */
+static int smi_get_sample(void *data)
+{
+	ktime_t start, t1, t2, spike;
+	s64 diff, total = 0;
+	u64 sample = 0;
+	struct smdata_struct *smi_data = (struct smdata_struct *)data;
+
+	start = ktime_get(); /* start timestamp */
+
+	do {
+
+		t1 = ktime_get();
+		t2 = ktime_get();
+
+		total = ktime_to_us(ktime_sub(t2, start));
+
+		diff = ktime_to_us(ktime_sub(t2, t1));
+		if (diff < 0) {
+			printk(KERN_ERR SMI_BANNER "time running backwards\n");
+			return 1;
+		}
+		if (diff > sample)
+			sample = diff; /* only want highest value per sample */
+
+		if (diff > smi_data->threshold)
+			spike = t1;
+
+	} while (total <= USEC_PER_MSEC*smi_sample_ms);
+
+	smi_data->last_sample = sample;
+
+	if (sample > smi_data->threshold) {
+		u64 tmp;
+
+		smi_data->smi_count++;
+		tmp = ktime_to_us(ktime_sub(spike, smi_data->last_spike));
+
+		if (smi_data->smi_count > 2)
+			smi_data->frequency = (smi_data->frequency + tmp) / 2;
+		else
+			if (smi_data->smi_count == 2)
+				smi_data->frequency = tmp;
+
+		smi_data->last_spike = spike;
+	}
+
+	atomic_set(&smi_data->pending, 1);
+
+	if (sample > smi_data->max_sample)
+		smi_data->max_sample = sample;
+
+	return 0;
+}
+
+/*
+ * smi_kthread_fn - Used to periodically sample the CPU TSC via smi_get_sample.
+ *                  We use stop_machine, which intentionally introduces latency.
+ */
+
+static int smi_kthread_fn(void *data)
+{
+	int err = 0;
+	struct smdata_struct *smi_data = (struct smdata_struct *)data;
+
+	while (!kthread_should_stop()) {
+		err = stop_machine(smi_get_sample, smi_data, 0);
+
+		wake_up(&smi_data->wq);
+
+		if (msleep_interruptible(smi_interval_ms))
+			goto out;
+	}
+
+out:
+	return 0;
+}
+
+struct task_struct *start_smi_thread(void)
+{
+	return smi_kthread = kthread_run(smi_kthread_fn, &smdata,
+					 "smi_detector");
+}
+
+void stop_smi_thread(void)
+{
+	if (smi_kthread)
+		kthread_stop(smi_kthread);
+}
+
+static int smi_debug_sample_fopen(struct inode *inode, struct file *filp)
+{
+
+	filp->private_data = (void *)&smdata;
+
+	return 0;
+}
+static ssize_t smi_debug_sample_fread(struct file *filp, char __user *ubuf,
+					size_t cnt, loff_t *ppos)
+{
+	int len;
+	char buf[64];
+	struct smdata_struct *smi_data = filp->private_data;
+
+	if (!enabled)
+		return 0;
+
+	wait_event_interruptible(smi_data->wq, atomic_read(&smi_data->pending));
+	atomic_set(&smi_data->pending, 0);
+	len = sprintf(buf, "%lld\n", smi_data->last_sample);
+	if (copy_to_user(ubuf, buf, len))
+		return -EFAULT;
+
+	return len;
+}
+
+static const struct file_operations smi_sample_fops = {
+	.open		= smi_debug_sample_fopen,
+	.read		= smi_debug_sample_fread,
+	.owner		= THIS_MODULE,
+};
+
+static int smi_debug_enable_fopen(struct inode *inode, struct file *filp)
+{
+	return 0;
+}
+
+
+static ssize_t smi_debug_enable_fread(struct file *filp, char __user *ubuf,
+				      size_t cnt, loff_t *ppos)
+{
+	char buffer[4];
+
+	if (!cnt || *ppos)
+		return 0;
+
+	buffer[0] = enabled ? '1' : '0';
+	buffer[1] = '\n';
+	buffer[2] = '\0';
+	if (copy_to_user(ubuf, buffer, 2))
+		return -EFAULT;
+	return *ppos = 2;
+}
+
+static ssize_t  smi_debug_enable_fwrite(struct file *file,
+					const char __user *user_buffer,
+					size_t user_size,
+					loff_t *offset)
+{
+	char buffer[4];
+	int copy_size = min(user_size, sizeof(buffer));
+	long val;
+
+	if (copy_from_user(buffer, user_buffer, copy_size))
+		return -EFAULT;
+#if 1
+	val = simple_strtol(buffer, NULL, 10);
+#else
+	if (strict_strtol(buffer, 10, &val))
+		return -EINVAL;
+#endif
+	mutex_lock(&enable_mutex);
+	if (val) {
+		if (enabled)
+			goto unlock;
+		smi_init_stats();
+		enabled = 1;
+		start_smi_thread();
+	} else {
+		if (!enabled)
+			goto unlock;
+		enabled = 0;
+		stop_smi_thread();
+	}
+unlock:
+	mutex_unlock(&enable_mutex);
+	printk(SMI_BANNER "smi_detector thread %s\n",
+		enabled ? "started" : "stopped");
+	return user_size;
+}
+
+static const struct file_operations smi_enable_fops = {
+	.open		= smi_debug_enable_fopen,
+	.read		= smi_debug_enable_fread,
+	.write		= smi_debug_enable_fwrite,
+	.owner		= THIS_MODULE,
+};
+
+/* debugfs_create_bool */
+int smi_detector_init(void)
+{
+
+	printk(KERN_INFO SMI_BANNER "version %s\n", smi_version);
+
+	smi_init_stats();
+
+	init_waitqueue_head(&smdata.wq);
+	atomic_set(&smdata.pending, 0);
+
+	smi_debug_dir = debugfs_create_dir("smi_detector", NULL);
+
+	if (smi_debug_dir == NULL) {
+		printk(KERN_INFO SMI_BANNER "debugfs not mounted!\n");
+		return -1;
+	}
+
+	smi_debug_sample_ms = debugfs_create_u32("ms_per_sample",
+				0644, smi_debug_dir, &smi_sample_ms);
+	smi_debug_interval_ms = debugfs_create_u32("ms_between_samples",
+				0644, smi_debug_dir, &smi_interval_ms);
+	smi_debug_max = debugfs_create_u64("max_sample_us",
+				0644, smi_debug_dir, &smdata.max_sample);
+	smi_debug_smi = debugfs_create_u64("smi_count",
+				0644, smi_debug_dir, &smdata.smi_count);
+	smi_debug_sample = debugfs_create_file("sample_us",
+				0444, smi_debug_dir, &smdata, &smi_sample_fops);
+	smi_debug_frequency_us = debugfs_create_u64("avg_smi_interval_us",
+				0444, smi_debug_dir, &smdata.frequency);
+	smi_debug_threshold = debugfs_create_u64("latency_threshold_us",
+				0444, smi_debug_dir, &smdata.threshold);
+
+	smi_debug_enable = debugfs_create_file("enable",
+				0644, smi_debug_dir,
+				&enabled, &smi_enable_fops);
+
+
+	if (enabled)
+		start_smi_thread();
+
+	return 0;
+}
+
+void smi_detector_exit(void)
+{
+	if (enabled) {
+		mutex_lock(&enable_mutex);
+		enabled = 0;
+		stop_smi_thread();
+		mutex_unlock(&enable_mutex);
+	}
+	if (smi_debug_sample_ms)
+		debugfs_remove(smi_debug_sample_ms);
+	if (smi_debug_interval_ms)
+		debugfs_remove(smi_debug_interval_ms);
+	if (smi_debug_max)
+		debugfs_remove(smi_debug_max);
+	if (smi_debug_smi)
+		debugfs_remove(smi_debug_smi);
+	if (smi_debug_frequency_us)
+		debugfs_remove(smi_debug_frequency_us);
+	if (smi_debug_threshold)
+		debugfs_remove(smi_debug_threshold);
+	if (smi_debug_sample)
+		debugfs_remove(smi_debug_sample);
+	if (smi_debug_enable)
+		debugfs_remove(smi_debug_enable);
+	if (smi_debug_dir)
+		debugfs_remove(smi_debug_dir);
+}
+
+module_init(smi_detector_init);
+module_exit(smi_detector_exit);
diff --git a/scripts/smidetect b/scripts/smidetect
new file mode 100644
index 0000000..81593a1
--- /dev/null
+++ b/scripts/smidetect
@@ -0,0 +1,282 @@
+#!/usr/bin/python
+
+import sys
+import os
+import time
+import subprocess
+
+version = "0.2"
+debugging = False
+#debugging = True
+
+# defaults for parameters
+default_threshold = 100 # 100us
+default_interval  =  10 # 10ms
+default_width     =   1 # 1ms
+
+def debug(str):
+    if debugging: print(str)
+
+class DebugFS(object):
+    '''class to manage the debugfs'''
+    def __init__(self):
+        self.premounted = False
+        self.mounted = False
+        self.mountpoint = ''
+        f = open('/proc/mounts')
+        for l in f:
+            field = l.split()
+            if field[2] == "debugfs":
+                self.premounted = True
+                self.mountpoint = field[1]
+                break
+        f.close()
+
+    def mount(self, path='/sys/kernel/debug'):
+        if self.premounted or self.mounted:
+            return True
+        self.mountpoint = path
+        cmd = ['/bin/mount', '-t', 'debugfs', 'none', path]
+        self.mounted = (subprocess.call(cmd) == 0)
+        return self.mounted
+
+    def umount(self):
+        if self.premounted or not self.mounted:
+            return True
+        cmd = ['/bin/umount', self.mountpoint]
+        self.mounted = not (subprocess.call(cmd) == 0)
+        return not self.mounted
+
+    def getval(self, item):
+        path = os.path.join(self.mountpoint, item)
+        f = open(path)
+        val = f.readline()
+        f.close()
+        return val
+
+    def putval(self, item, value):
+        path = os.path.join(self.mountpoint, item)
+        f = open(path, "w")
+        f.write(str(value))
+        f.close()
+
+class Kmod(object):
+    ''' class to manage loading and unloading smi_detector.ko'''
+    def __init__(self, module='smi_detector'):
+        self.modname = module
+        self.preloaded = False
+        f = open ('/proc/modules')
+        for l in f:
+            field = l.split()
+            if field[0] == self.modname:
+                self.preloaded = True
+                break
+        f.close
+
+    def load(self):
+        if self.preloaded:
+            return True
+        cmd = ['/sbin/modprobe', self.modname]
+        return (subprocess.call(cmd) == 0)
+
+    def unload(self):
+        if self.preloaded:
+            return True
+        cmd = ['/sbin/modprobe', '-r', self.modname]
+        return (subprocess.call(cmd) == 0)
+
+class SMI_Detector(object):
+    '''class to wrap access to smi_detector debugfs files'''
+    def __init__(self):
+        if os.getuid() != 0:
+            raise RuntimeError, "Must be root"
+        self.debugfs = DebugFS()
+        self.kmod = Kmod()
+        self.setup()
+        self.testduration = 10 # ten seconds
+        self.samples = []
+
+    def force_cleanup(self):
+        debug("forcing unload of smi_detector module")
+        self.kmod.preloaded = False
+        debug("forcing unmount of debugfs")
+        self.debugfs.premounted = False
+        self.cleanup()
+        debug("exiting")
+        sys.exit(0)
+
+    def setup(self):
+        if not self.debugfs.mount():
+            raise RuntimeError, "Failed to mount debugfs"
+        if not self.kmod.load():
+            raise RuntimeError, "Failed to unload smi_detector"
+
+    def cleanup(self):
+        if not self.kmod.unload():
+            raise RuntimeError, "Failed to unload smi_detector"
+        if not self.debugfs.umount():
+            raise RuntimeError, "Failed to unmount debugfs"
+
+    def get_avg_smi_interval(self):
+        return int(self.debugfs.getval("smi_detector/avg_smi_interval"))
+
+    def set_agv_smi_interval(self, interval):
+        self.debugfs.putval("smi_detector/avg_smi_interval", str(interval))
+
+    def get_enable(self):
+        return int(self.debugfs.getval("smi_detector/enable"))
+
+    def set_enable(self, value):
+        self.debugfs.putval("smi_detector/enable", value)
+
+    def get_latency_threshold_us(self):
+        return int(self.debugfs.getval("smi_detector/latency_threshold_us"))
+
+    def set_latency_threshold_us(self, value):
+        self.debugfs.putval("smi_detector/latency_threshold_us", value)
+
+    def get_max_sample_us(self):
+        return int(self.debugfs.getval("smi_detector/max_sample_us"))
+
+    def set_max_sample_us(self, value):
+        self.debugfs.putval("smi_detector/max_sample_us", value)
+
+    def get_ms_between_samples(self):
+        return int(self.debugfs.getval("smi_detector/ms_between_samples"))
+
+    def set_ms_between_samples(self, value):
+        self.debugfs.putval("smi_detector/ms_between_samples", value)
+
+    def get_ms_per_sample(self):
+        return int(self.debugfs.getval("smi_detector/ms_per_sample"))
+
+    def set_ms_per_sample(self, value):
+        self.debugfs.putval("smi_detector/ms_per_sample", value)
+
+    def get_sample_us(self):
+        return int(self.debugfs.getval("smi_detector/sample_us"))
+
+    def get_smi_count(self):
+        return int(self.debugfs.getval("smi_detector/smi_count"))
+
+    def start(self):
+        self.set_enable(1)
+
+    def stop(self):
+        self.set_enable(0)
+        while self.get_enable() == 1:
+            time.sleep(0.1)
+            self.set_enable(0)
+
+    def detect(self):
+        self.samples = []
+        testend = time.time() + self.testduration
+        debug("Starting SMI detection for %d seconds" % (self.testduration))
+        try:
+            self.start()
+            while time.time() < testend:
+                val = self.get_sample_us()
+                self.samples.append(val)
+        finally:
+            debug("Stopping SMI detection")
+            self.stop()
+        debug("SMI detection done (%d samples)" % len(self.samples))
+
+if __name__ == '__main__':
+    from optparse import OptionParser
+
+    parser = OptionParser()
+    parser.add_option("--duration", default=None, type="string",
+                      dest="duration",
+                      help="total time to test for SMIs (seconds)")
+
+    parser.add_option("--threshold", default=None, type="string",
+                      dest="threshold",
+                      help="value above which is considered an SMI (microseconds)")
+
+    parser.add_option("--interval", default=None, type="string",
+                      dest="interval",
+                      help="time between samples (milliseconds)")
+
+    parser.add_option("--sample_width", default=None, type="string",
+                      dest="sample_width",
+                      help="time to actually measure (milliseconds)")
+
+    parser.add_option("--report", default=None, type="string",
+                      dest="report",
+                      help="filename for sample data")
+
+    parser.add_option("--stdout", action="store_true", default=False,
+                      dest="stdout",
+                      help="send sample data to stdout")
+
+    parser.add_option("--cleanup", action="store_true", default=False,
+                      dest="cleanup",
+                      help="force unload of module and umount of debugfs")
+
+#    parser.add_option("--walk", action="store_true", default=False,
+#                      dest="walk")
+
+    (o, a) = parser.parse_args()
+
+    smi = SMI_Detector()
+
+    if o.cleanup:
+        debug("forcing cleanup of debugfs and SMI module")
+        smi.force_cleanup()
+        sys.exit(0)
+
+    if o.threshold:
+        t = int(o.threshold)
+        smi.set_latency_threshold_us(t)
+    else:
+	smi.set_latency_threshold_us(default_threshold)
+
+    if o.interval:
+        i = int(o.interval)
+        smi.set_ms_between_samples(i)
+    else:
+	smi.set_ms_between_samples(default_interval)
+
+    if o.sample_width:
+        w = int(o.sample_width)
+        smi.set_ms_per_sample(w)
+    else:
+	smi.set_ms_per_sample(default_width)
+
+    if o.duration:
+        smi.testduration = int(o.duration)
+    else:
+        smi.testduration = 120 # 2 minutes
+
+    reportfile = o.report
+    if not reportfile:
+        reportfile = 'smidetect.txt'
+    stdout = o.stdout
+
+    print "smidetect:  test duration %d seconds" % smi.testduration
+    print "   parameters:"
+    print "        Latency threshold: %dus" % smi.get_latency_threshold_us()
+    print "        Sample interval:   %dms" % smi.get_ms_between_samples()
+    print "        Sample length:     %dms" % smi.get_ms_per_sample()
+    print "        Output File:       %s" % reportfile
+    print "\nStarting test"
+
+    smi.detect()
+
+    print "test finished"
+    print "Max Latency: %dus" % smi.get_max_sample_us()
+    print "Samples exceeding threshold: %d" % smi.get_smi_count()
+
+    if stdout:
+        for s in smi.samples:
+            print "%d" % s
+
+    if reportfile:
+        f = open(reportfile, "w")
+        for s in smi.samples:
+            f.write("%d\n" % s)
+        f.close()
+        print "sample data written to %s" % reportfile
+
+    smi.cleanup()
-- 
1.6.0.6

Re: [PATCH 1/2] SMI Detector: a simple module for detecting System Management Interrupts

[Frédéric Weisbecker]

Hi,


2009/4/2 Jon Masters <jcm@jonmasters.org>:
> System Management Interrupts (SMIs) are a feature of modern x86-compatible
> microprocessors. They allow BIOS provided management code to "borrow" the
> system CPU in order to perform certain activities - device emulation,
> thermal throttling, fan control, and similar. The CPU exposes the SMI
> functionality through a dedicated pin and special purpose logic. When an
> SMI is asserted, the CPU suspends the overlying running Operating System
> and executes special SMI management routines within a unique context.
>
> SMI routines are usually provided by the system BIOS, and the SMI assertion
> is usually made by logic in the system's South Bridge. The Operating System
> is typically completely unaware of the presence of an SMI, much less the
> amount of time spent handling them. Therein lies the problem. Some of these
> SMI routines can take many milliseconds to complete (or even longer,
> depending upon the implementation of the routines). Although it is possible
> to disable SMIs (typically by poking at the South Bridge LPC or similar),
> that can be *EXTREMELY DANGEROUS* because it can result in a system
> overheating, or even worse. Therefore, we simply try to detect them. We do
> not attempt to disable them and discourage other efforts at doing so. We
> instead prefer to collate data and ask BIOS vendors to fix their code.
>
> We have been increasingly concerned about the amount of time certain systems
> spend inside System Management Interrupt (SMI) routines, especially on those
> systems intended for "real time" applications. This module can be used to
> detect SMIs as they occur by periodically grabbing the CPU(s) within a
> stop_machine context, and sitting in a tight loop reading the timestamp
> counter during the monitoring phase. If we experience unexplained
> discontiguous readings in the CPU timestamps, we are able to assert the
> presence of an SMI condition (the CPU is doing nothing else at the time).
>
> Since we steal the CPU for relatively long periods of time, this module is
> intended primarily for diagnostic use. It should not be used in a normal
> production environment unless "enable" is set to zero or the acquisition
> parameters are set sufficiently low to avoid performance impact.
>
> There are a number of pending feature improvements to this code but we
> would like to get it out there and in use tracking down SMIs.
>
> Signed-off-by: Jon Masters <jcm@jonmasters.org>
> ---
>  Documentation/smi_detector.txt |   94 +++++++++++
>  drivers/misc/Kconfig           |   14 ++
>  drivers/misc/Makefile          |    1 +
>  drivers/misc/smi_detector.c    |  360 ++++++++++++++++++++++++++++++++++++++++
>  scripts/smidetect              |  282 +++++++++++++++++++++++++++++++
>  5 files changed, 751 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/smi_detector.txt
>  create mode 100644 drivers/misc/smi_detector.c
>  create mode 100644 scripts/smidetect
>
> diff --git a/Documentation/smi_detector.txt b/Documentation/smi_detector.txt
> new file mode 100644
> index 0000000..902ff36
> --- /dev/null
> +++ b/Documentation/smi_detector.txt
> @@ -0,0 +1,94 @@
> +Introduction:
> +-------------
> +
> +The module smi_detector is a special purpose kernel module that is
> +used to detect if System Management Interrupts (SMIs) are causing event
> +latencies in the Linux RT kernel.
> +
> +SMIs are usually not serviced by the Linux kernel. They are set up by
> +BIOS code and are serviced by BIOS code, usually for critical events
> +such as management of thermal sensors and fans. Sometimes though, SMIs
> +are used for other tasks and those tasks can spend an inordinate
> +amount of time in the handler (sometimes measured in milliseconds).
> +Obviously if you are trying to keep event service latencies down in the
> +microsecond range, this is a problem.
> +
> +The SMI detector works by hogging the cpu for configurable amounts of
> +time (by calling stop_machine()), polling the Time Stamp Counter (TSC)
> +register for some period, then looking for gaps in the TSC data. Any
> +gap indicates a time when the polling was interrupted and since the
> +machine is stopped and interrupts turned off the only thing that could
> +do that would be an SMI.
> +
> +Note that the SMI detector should *NEVER* be used in a production
> +environment. It is intended to be run manually to determine if the
> +hardware platform has a problem with long SMI service routines.
> +
> +Usage:
> +------
> +
> +Loading the module smi_detector passing the parameter "enabled=1" is the only
> +step required to start the smi_detector. It is possible to define a threshold
> +in microseconds (us) above which latency spikes will be taken in account
> +(parameter "threshold=").
> +
> +Example:
> +
> +       # insmod ./smi_detector.ko enabled=1 threshold=100
> +
> +After the module is loaded, it creates a directory named "smi_detector" under
> +the debugfs mountpoint, "/debugfs/smi_detector" for this text. It is necessary
> +to have debugfs mounted.
> +
> +avg_smi_interval_us    - average interval (usecs) between SMI latency spikes
> +latency_threshold_us   - minimum latency value to be considered (usecs)
> +max_sample_us          - maximum SMI latency spike observed (usecs)
> +ms_between_samples     - interval between samples (ms)
> +ms_per_sample          - sampling time (ms)
> +sample_us              - last sample (usecs). Continously updated, may be used
> +                         to plot graphs or to create histograms
> +smi_count              - how many latency spikes have been observed
> +
> +
> +       # cd /debugfs/smi_detector
> +
> +       # cat *
> +       0               (avg_smi_interval_us)
> +       100             (latency_threshold_us)
> +       0               (latency_threshold_us)
> +       5000            (ms_between_samples)
> +       1               (ms_per_sample)
> +       3               (sample_us)
> +       0               (smi_count)
> +
> +
> +The default values for ms_between_samples and ms_per_sample define that every
> +5000ms (5s) samples will be collected during 1ms. It is possible to change the
> +sampling time or the sampling interval writing to the related files. To collect
> +samples during 5ms every 50ms:
> +
> +       # echo 5 > ms_per_sample
> +       # echo 50 > ms_between_samples
> +
> +
> +       # cat ms_between_samples
> +       50
> +       # cat ms_per_sample
> +       5
> +
> +After a while, data may be verified to atest the existence of SMI induced
> +latencies:
> +
> +       # cat smi_count
> +       2
> +       # cat max_sample_us
> +       468
> +       # cat avg_smi_interval_us
> +       1356306050
> +
> +Depending on the latencies observed it is important to better adjust the
> +sampling intervals to obtain more accurate measurements. Care must be taken
> +to not create a continous sampling situation, that might be perceived by the
> +kernel as a deadlock.


Btw, you should perhaps add a check to ensure the user hasn't set a
dangerous pair value in ms_per_sample/ms_between_sample

The simple case of ms_per_sample == ms_between_sample will
hang the box. Just a check like:

if (ms_between_sample - ms_per_sample < 100)
      // not good

So that your ensure the system keeps at least 100 ms to run outside
the smi detector.


> +
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 1c48408..573ae2e 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -76,6 +76,20 @@ config IBM_ASM
>          information on the specific driver level and support statement
>          for your IBM server.
>
> +config SMI_DETECTOR
> +       tristate "Test module for detecting time gaps caused by SMIs"
> +       default m
> +       ---help---
> +         A simple SMI detector. Use this module to detect large system
> +         latencies introduced by the presence of vendor BIOS SMI
> +         (System Management Interrupts) somehow gone awry. We do this
> +         by hogging all of the CPU(s) for configurable time intervals,
> +         looking to see if something stole time from us. Therefore,
> +         obviously, you should NEVER use this module in a production
> +         environment.
> +
> +         If unsure, say N
> +
>  config PHANTOM
>        tristate "Sensable PHANToM (PCI)"
>        depends on PCI
> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> index bc11998..7f23e02 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -20,3 +20,4 @@ obj-$(CONFIG_SGI_GRU)         += sgi-gru/
>  obj-$(CONFIG_HP_ILO)           += hpilo.o
>  obj-$(CONFIG_C2PORT)           += c2port/
>  obj-y                          += eeprom/
> +obj-$(CONFIG_SMI_DETECTOR)     += smi_detector.o
> diff --git a/drivers/misc/smi_detector.c b/drivers/misc/smi_detector.c
> new file mode 100644
> index 0000000..40913fc
> --- /dev/null
> +++ b/drivers/misc/smi_detector.c
> @@ -0,0 +1,360 @@
> +/*
> + * A simple SMI detector. Use this module to detect large system latencies
> + * introduced by the presence of vendor BIOS SMI (System Management Interrupts)
> + * somehow gone awry. We do this by hogging all of the CPU(s) for configurable
> + * time intervals, looking to see if something stole time from us. Therefore,
> + * obviously, you should NEVER use this module in a production environment.
> + *
> + * Copyright (C) 2008 Jon Masters, Red Hat, Inc. <jcm@redhat.com>
> + *
> + * Miscelleaneous tweaks:  Clark Williams <williams@redhat.com>
> + *
> + * Licensed under the GNU General Public License, version 2.0.
> + *
> + */
> +
> +#include <linux/module.h>
> +#include <linux/init.h>
> +
> +#include <linux/stop_machine.h>
> +#include <linux/time.h>
> +#include <linux/hrtimer.h>
> +#include <linux/kthread.h>
> +#include <linux/debugfs.h>
> +#include <linux/seq_file.h>
> +#include <linux/uaccess.h>
> +#include <linux/version.h>
> +
> +/*
> + * The below version code is the code of the git commit where
> + * stop_machine replaced stop_machine_run
> + */
> +/*#if LINUX_VERSION_CODE < 132637*/
> +#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 28)
> +#define stop_machine  stop_machine_run
> +#endif
> +
> +#define smi_version "0.3.0"
> +#define SMI_BANNER "SMI Detector: "
> +#define DEFAULT_MS_PER_SAMPLE 1    /* milliseconds */
> +#define DEFAULT_MS_SEP_SAMPLE 50   /* milliseconds */
> +#define DEFAULT_SMI_THRESHOLD 10   /* microseconds */
> +
> +MODULE_AUTHOR("Jon Masters <jcm@redhat.com>");
> +MODULE_DESCRIPTION("A simple SMI detector");
> +MODULE_LICENSE("GPL");
> +
> +static int debug;
> +static int enabled;
> +static int threshold;
> +
> +module_param(debug, int, 0);
> +module_param(enabled, int, 0);
> +module_param(threshold, int, 0);
> +
> +DEFINE_MUTEX(enable_mutex);
> +
> +struct task_struct *smi_kthread;
> +
> +struct smdata_struct {
> +
> +       u64     last_sample;
> +       u64     max_sample;
> +       u64     smi_count;
> +       u64     threshold;
> +       ktime_t last_spike;
> +       u64     frequency;
> +
> +       atomic_t pending;
> +       wait_queue_head_t wq;
> +
> +} smdata;
> +
> +static void smi_init_stats(void)
> +{
> +       smdata.last_sample = 0;
> +       smdata.max_sample = 0;
> +       smdata.smi_count = 0;
> +       smdata.frequency = 0;
> +       smdata.threshold = threshold ? threshold : DEFAULT_SMI_THRESHOLD;
> +}
> +
> +
> +struct dentry *smi_debug_dir;          /* SMI debugfs directory */
> +struct dentry *smi_debug_max;          /* maximum TSC delta */
> +struct dentry *smi_debug_smi;          /* SMI detect count */
> +struct dentry *smi_debug_sample_ms;    /* sample size ms */
> +struct dentry *smi_debug_interval_ms;  /* interval size ms */
> +struct dentry *smi_debug_sample;       /* raw SMI samples (us) */
> +struct dentry *smi_debug_threshold;    /* latency threshold (us) */
> +struct dentry *smi_debug_frequency_us; /* avg smi spike interval (us) */
> +struct dentry *smi_debug_enable;       /* enable/disable smi detection */
> +
> +u32 smi_sample_ms   = DEFAULT_MS_PER_SAMPLE;    /* sample size ms */
> +u32 smi_interval_ms = DEFAULT_MS_SEP_SAMPLE;    /* interval size ms */
> +
> +/*
> + * smi_get_sample -    Used to repeatedly capture the CPU TSC (or similar),
> + *                      looking for potential SMIs. Called under stop_machine.
> + */
> +static int smi_get_sample(void *data)
> +{
> +       ktime_t start, t1, t2, spike;
> +       s64 diff, total = 0;
> +       u64 sample = 0;
> +       struct smdata_struct *smi_data = (struct smdata_struct *)data;
> +
> +       start = ktime_get(); /* start timestamp */
> +
> +       do {
> +
> +               t1 = ktime_get();



So this is the window of SMI's detection.
It is rather tiny but I guess that's the only solution.

But if t2 is far enough from t1, it could also mean that
the tsc is unstable, right?

Also, does ktime_get() always take the tsc as its clocksource?



> +               t2 = ktime_get();
> +
> +               total = ktime_to_us(ktime_sub(t2, start));
> +
> +               diff = ktime_to_us(ktime_sub(t2, t1));
> +               if (diff < 0) {
> +                       printk(KERN_ERR SMI_BANNER "time running backwards\n");
> +                       return 1;
> +               }
> +               if (diff > sample)
> +                       sample = diff; /* only want highest value per sample */
> +
> +               if (diff > smi_data->threshold)
> +                       spike = t1;
> +
> +       } while (total <= USEC_PER_MSEC*smi_sample_ms);
> +
> +       smi_data->last_sample = sample;
> +
> +       if (sample > smi_data->threshold) {
> +               u64 tmp;
> +
> +               smi_data->smi_count++;
> +               tmp = ktime_to_us(ktime_sub(spike, smi_data->last_spike));
> +
> +               if (smi_data->smi_count > 2)
> +                       smi_data->frequency = (smi_data->frequency + tmp) / 2;
> +               else
> +                       if (smi_data->smi_count == 2)
> +                               smi_data->frequency = tmp;
> +
> +               smi_data->last_spike = spike;
> +       }
> +
> +       atomic_set(&smi_data->pending, 1);
> +
> +       if (sample > smi_data->max_sample)
> +               smi_data->max_sample = sample;
> +
> +       return 0;
> +}
> +
> +/*
> + * smi_kthread_fn - Used to periodically sample the CPU TSC via smi_get_sample.
> + *                  We use stop_machine, which intentionally introduces latency.
> + */
> +
> +static int smi_kthread_fn(void *data)
> +{
> +       int err = 0;
> +       struct smdata_struct *smi_data = (struct smdata_struct *)data;
> +
> +       while (!kthread_should_stop()) {
> +               err = stop_machine(smi_get_sample, smi_data, 0);
> +
> +               wake_up(&smi_data->wq);
> +
> +               if (msleep_interruptible(smi_interval_ms))
> +                       goto out;
> +       }
> +
> +out:
> +       return 0;
> +}
> +
> +struct task_struct *start_smi_thread(void)
> +{
> +       return smi_kthread = kthread_run(smi_kthread_fn, &smdata,
> +                                        "smi_detector");
> +}
> +
> +void stop_smi_thread(void)
> +{
> +       if (smi_kthread)
> +               kthread_stop(smi_kthread);
> +}
> +
> +static int smi_debug_sample_fopen(struct inode *inode, struct file *filp)
> +{
> +
> +       filp->private_data = (void *)&smdata;
> +
> +       return 0;
> +}
> +static ssize_t smi_debug_sample_fread(struct file *filp, char __user *ubuf,
> +                                       size_t cnt, loff_t *ppos)
> +{
> +       int len;
> +       char buf[64];
> +       struct smdata_struct *smi_data = filp->private_data;
> +
> +       if (!enabled)
> +               return 0;
> +
> +       wait_event_interruptible(smi_data->wq, atomic_read(&smi_data->pending));
> +       atomic_set(&smi_data->pending, 0);
> +       len = sprintf(buf, "%lld\n", smi_data->last_sample);
> +       if (copy_to_user(ubuf, buf, len))
> +               return -EFAULT;
> +
> +       return len;
> +}
> +
> +static const struct file_operations smi_sample_fops = {
> +       .open           = smi_debug_sample_fopen,
> +       .read           = smi_debug_sample_fread,
> +       .owner          = THIS_MODULE,
> +};
> +
> +static int smi_debug_enable_fopen(struct inode *inode, struct file *filp)
> +{
> +       return 0;
> +}
> +
>


Debugs already provides such stub callbacks if you don't give any.



> +static ssize_t smi_debug_enable_fread(struct file *filp, char __user *ubuf,
> +                                     size_t cnt, loff_t *ppos)
> +{
> +       char buffer[4];
> +
> +       if (!cnt || *ppos)
> +               return 0;
> +
> +       buffer[0] = enabled ? '1' : '0';
> +       buffer[1] = '\n';
> +       buffer[2] = '\0';
> +       if (copy_to_user(ubuf, buffer, 2))
> +               return -EFAULT;
> +       return *ppos = 2;
> +}
> +
> +static ssize_t  smi_debug_enable_fwrite(struct file *file,
> +                                       const char __user *user_buffer,
> +                                       size_t user_size,
> +                                       loff_t *offset)
> +{
> +       char buffer[4];
> +       int copy_size = min(user_size, sizeof(buffer));
> +       long val;
> +
> +       if (copy_from_user(buffer, user_buffer, copy_size))
> +               return -EFAULT;
> +#if 1
> +       val = simple_strtol(buffer, NULL, 10);
> +#else
> +       if (strict_strtol(buffer, 10, &val))
> +               return -EINVAL;
> +#endif



So I guess the #else statement can disappear? :-)



> +       mutex_lock(&enable_mutex);
> +       if (val) {
> +               if (enabled)
> +                       goto unlock;
> +               smi_init_stats();
> +               enabled = 1;
> +               start_smi_thread();
> +       } else {
> +               if (!enabled)
> +                       goto unlock;
> +               enabled = 0;
> +               stop_smi_thread();
> +       }
> +unlock:
> +       mutex_unlock(&enable_mutex);
> +       printk(SMI_BANNER "smi_detector thread %s\n",
> +               enabled ? "started" : "stopped");
> +       return user_size;
> +}
> +
> +static const struct file_operations smi_enable_fops = {
> +       .open           = smi_debug_enable_fopen,
> +       .read           = smi_debug_enable_fread,
> +       .write          = smi_debug_enable_fwrite,
> +       .owner          = THIS_MODULE,
> +};
> +
> +/* debugfs_create_bool */
> +int smi_detector_init(void)
> +{
> +
> +       printk(KERN_INFO SMI_BANNER "version %s\n", smi_version);
> +
> +       smi_init_stats();
> +
> +       init_waitqueue_head(&smdata.wq);
> +       atomic_set(&smdata.pending, 0);
> +
> +       smi_debug_dir = debugfs_create_dir("smi_detector", NULL);
> +
> +       if (smi_debug_dir == NULL) {
> +               printk(KERN_INFO SMI_BANNER "debugfs not mounted!\n");
> +               return -1;
> +       }
> +
> +       smi_debug_sample_ms = debugfs_create_u32("ms_per_sample",
> +                               0644, smi_debug_dir, &smi_sample_ms);
> +       smi_debug_interval_ms = debugfs_create_u32("ms_between_samples",
> +                               0644, smi_debug_dir, &smi_interval_ms);
> +       smi_debug_max = debugfs_create_u64("max_sample_us",
> +                               0644, smi_debug_dir, &smdata.max_sample);
> +       smi_debug_smi = debugfs_create_u64("smi_count",
> +                               0644, smi_debug_dir, &smdata.smi_count);
> +       smi_debug_sample = debugfs_create_file("sample_us",
> +                               0444, smi_debug_dir, &smdata, &smi_sample_fops);
> +       smi_debug_frequency_us = debugfs_create_u64("avg_smi_interval_us",
> +                               0444, smi_debug_dir, &smdata.frequency);
> +       smi_debug_threshold = debugfs_create_u64("latency_threshold_us",
> +                               0444, smi_debug_dir, &smdata.threshold);
> +
> +       smi_debug_enable = debugfs_create_file("enable",
> +                               0644, smi_debug_dir,
> +                               &enabled, &smi_enable_fops);
> +
> +
> +       if (enabled)
> +               start_smi_thread();
> +
> +       return 0;
> +}
> +
> +void smi_detector_exit(void)
> +{
> +       if (enabled) {
> +               mutex_lock(&enable_mutex);
> +               enabled = 0;
> +               stop_smi_thread();
> +               mutex_unlock(&enable_mutex);
> +       }
> +       if (smi_debug_sample_ms)
> +               debugfs_remove(smi_debug_sample_ms);
> +       if (smi_debug_interval_ms)
> +               debugfs_remove(smi_debug_interval_ms);
> +       if (smi_debug_max)
> +               debugfs_remove(smi_debug_max);
> +       if (smi_debug_smi)
> +               debugfs_remove(smi_debug_smi);
> +       if (smi_debug_frequency_us)
> +               debugfs_remove(smi_debug_frequency_us);
> +       if (smi_debug_threshold)
> +               debugfs_remove(smi_debug_threshold);
> +       if (smi_debug_sample)
> +               debugfs_remove(smi_debug_sample);
> +       if (smi_debug_enable)
> +               debugfs_remove(smi_debug_enable);
> +       if (smi_debug_dir)
> +               debugfs_remove(smi_debug_dir);



You can also use debugfs_remove_recursive()



> +}
> +
> +module_init(smi_detector_init);
> +module_exit(smi_detector_exit);
> diff --git a/scripts/smidetect b/scripts/smidetect
> new file mode 100644
> index 0000000..81593a1
> --- /dev/null
> +++ b/scripts/smidetect


The script should be in a separate patch, no?

Thanks,
Frederic.

Re: [PATCH 1/2] SMI Detector: a simple module for detecting System Management Interrupts

[Clark Williams]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Thu, 2 Apr 2009 21:05:26 +0200
Frédéric Weisbecker <fweisbec@gmail.com> wrote:


> > +#if 1
> > +       val = simple_strtol(buffer, NULL, 10);
> > +#else
> > +       if (strict_strtol(buffer, 10, &val))
> > +               return -EINVAL;
> > +#endif
> 
> 
> 
> So I guess the #else statement can disappear? :-)
> 
> 

Ugh, don't blame Jon for that. I was trying to get rid of some
checkpatch warnings and was experimenting with strict vs. simple
strtol. 

I'll clean that up in the next iteration. Or Jon can and will then
abuse me :)

Clark

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Re: [PATCH 1/2] SMI Detector: a simple module for detecting System Management Interrupts

[Jon Masters]

Thanks Clark and Frederic. I am currently on a train going through the  
Rockies but will send an update tomorrow. Sorry for top posting.

Jon.



On Apr 2, 2009, at 14:16, Clark Williams <williams@redhat.com> wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On Thu, 2 Apr 2009 21:05:26 +0200
> Frédéric Weisbecker <fweisbec@gmail.com> wrote:
>
>
>>> +#if 1
>>> +       val = simple_strtol(buffer, NULL, 10);
>>> +#else
>>> +       if (strict_strtol(buffer, 10, &val))
>>> +               return -EINVAL;
>>> +#endif
>>
>>
>>
>> So I guess the #else statement can disappear? :-)
>>
>>
>
> Ugh, don't blame Jon for that. I was trying to get rid of some
> checkpatch warnings and was experimenting with strict vs. simple
> strtol.
>
> I'll clean that up in the next iteration. Or Jon can and will then
> abuse me :)
>
> Clark
>
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v2.0.9 (GNU/Linux)
>
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> OycAn1Nl1OQr7nPUxPp3rln5SYVE4Bcn
> =kZRN
> -----END PGP SIGNATURE-----

Re: [PATCH 1/2] SMI Detector: a simple module for detecting System Management Interrupts

[Andrew Morton]

On Thu,  2 Apr 2009 12:50:04 -0400
Jon Masters <jcm@jonmasters.org> wrote:

> System Management Interrupts (SMIs) are a feature of modern x86-compatible
> microprocessors. They allow BIOS provided management code to "borrow" the
> system CPU in order to perform certain activities - device emulation,
> thermal throttling, fan control, and similar. The CPU exposes the SMI
> functionality through a dedicated pin and special purpose logic. When an
> SMI is asserted, the CPU suspends the overlying running Operating System
> and executes special SMI management routines within a unique context.
> 
> SMI routines are usually provided by the system BIOS, and the SMI assertion
> is usually made by logic in the system's South Bridge. The Operating System
> is typically completely unaware of the presence of an SMI, much less the
> amount of time spent handling them. Therein lies the problem. Some of these
> SMI routines can take many milliseconds to complete (or even longer,
> depending upon the implementation of the routines). Although it is possible
> to disable SMIs (typically by poking at the South Bridge LPC or similar),
> that can be *EXTREMELY DANGEROUS* because it can result in a system
> overheating, or even worse. Therefore, we simply try to detect them. We do
> not attempt to disable them and discourage other efforts at doing so. We
> instead prefer to collate data and ask BIOS vendors to fix their code.
> 
> We have been increasingly concerned about the amount of time certain systems
> spend inside System Management Interrupt (SMI) routines, especially on those
> systems intended for "real time" applications. This module can be used to
> detect SMIs as they occur by periodically grabbing the CPU(s) within a
> stop_machine context, and sitting in a tight loop reading the timestamp
> counter during the monitoring phase. If we experience unexplained
> discontiguous readings in the CPU timestamps, we are able to assert the
> presence of an SMI condition (the CPU is doing nothing else at the time).
> 
> Since we steal the CPU for relatively long periods of time, this module is
> intended primarily for diagnostic use. It should not be used in a normal
> production environment unless "enable" is set to zero or the acquisition
> parameters are set sufficiently low to avoid performance impact.
> 
> There are a number of pending feature improvements to this code but we
> would like to get it out there and in use tracking down SMIs.
> 
>
> ...
>
> +config SMI_DETECTOR
> +	tristate "Test module for detecting time gaps caused by SMIs"
> +	default m
> +	---help---
> +	  A simple SMI detector. Use this module to detect large system
> +	  latencies introduced by the presence of vendor BIOS SMI
> +	  (System Management Interrupts) somehow gone awry. We do this
> +	  by hogging all of the CPU(s) for configurable time intervals,
> +	  looking to see if something stole time from us. Therefore,
> +	  obviously, you should NEVER use this module in a production
> +	  environment.
> +
> +	  If unsure, say N

Does this have enough dependencies?  I have a feeling that the driver
won't work well on mips..  CONFIG_DEBUGFS?  Others?

>
> ...
>
> +module_param(debug, int, 0);
> +module_param(enabled, int, 0);
> +module_param(threshold, int, 0);
> +
> +DEFINE_MUTEX(enable_mutex);

static, please.

> +struct task_struct *smi_kthread;

ditto.

> +struct smdata_struct {
> +
> +	u64	last_sample;
> +	u64	max_sample;
> +	u64	smi_count;
> +	u64	threshold;
> +	ktime_t last_spike;
> +	u64	frequency;
> +
> +	atomic_t pending;
> +	wait_queue_head_t wq;
> +
> +} smdata;

Carefully documenting each of the above fields would be of assistance
to others.

> +static void smi_init_stats(void)
> +{
> +	smdata.last_sample = 0;
> +	smdata.max_sample = 0;
> +	smdata.smi_count = 0;
> +	smdata.frequency = 0;
> +	smdata.threshold = threshold ? threshold : DEFAULT_SMI_THRESHOLD;
> +}
> +
> +
> +struct dentry *smi_debug_dir;		/* SMI debugfs directory */
> +struct dentry *smi_debug_max;		/* maximum TSC delta */
> +struct dentry *smi_debug_smi;		/* SMI detect count */
> +struct dentry *smi_debug_sample_ms;	/* sample size ms */
> +struct dentry *smi_debug_interval_ms;	/* interval size ms */
> +struct dentry *smi_debug_sample;	/* raw SMI samples (us) */
> +struct dentry *smi_debug_threshold;	/* latency threshold (us) */
> +struct dentry *smi_debug_frequency_us;	/* avg smi spike interval (us) */
> +struct dentry *smi_debug_enable;	/* enable/disable smi detection */
> +
> +u32 smi_sample_ms   = DEFAULT_MS_PER_SAMPLE;    /* sample size ms */
> +u32 smi_interval_ms = DEFAULT_MS_SEP_SAMPLE;    /* interval size ms */

Did these all need to be global symbols?

> +/*
> + * smi_get_sample -	Used to repeatedly capture the CPU TSC (or similar),
> + *                      looking for potential SMIs. Called under stop_machine.
> + */
> +static int smi_get_sample(void *data)
> +{
> +	ktime_t start, t1, t2, spike;
> +	s64 diff, total = 0;
> +	u64 sample = 0;
> +	struct smdata_struct *smi_data = (struct smdata_struct *)data;

Unneeded and undesirable cast of void*.

> +	start = ktime_get(); /* start timestamp */
> +
> +	do {
> +
> +		t1 = ktime_get();
> +		t2 = ktime_get();

I'd have expected to see a local_irq_disable() around these two samplings.

> +		total = ktime_to_us(ktime_sub(t2, start));
> +
> +		diff = ktime_to_us(ktime_sub(t2, t1));
> +		if (diff < 0) {
> +			printk(KERN_ERR SMI_BANNER "time running backwards\n");
> +			return 1;
> +		}
> +		if (diff > sample)
> +			sample = diff; /* only want highest value per sample */
> +
> +		if (diff > smi_data->threshold)
> +			spike = t1;
> +
> +	} while (total <= USEC_PER_MSEC*smi_sample_ms);

Naive question: should we be using nanoseconds here rather than rather
coarse microseconds?


> +	smi_data->last_sample = sample;
> +
> +	if (sample > smi_data->threshold) {
> +		u64 tmp;

eek.  `tmp' is a wicked identifier.  Can we choose something more meaningful?

> +		smi_data->smi_count++;
> +		tmp = ktime_to_us(ktime_sub(spike, smi_data->last_spike));
> +
> +		if (smi_data->smi_count > 2)
> +			smi_data->frequency = (smi_data->frequency + tmp) / 2;
> +		else
> +			if (smi_data->smi_count == 2)
> +				smi_data->frequency = tmp;
> +
> +		smi_data->last_spike = spike;
> +	}
> +
> +	atomic_set(&smi_data->pending, 1);

See, this code would be more easy to review if you'd told us what
`pending' does.

> +	if (sample > smi_data->max_sample)
> +		smi_data->max_sample = sample;
> +
> +	return 0;
> +}
> +
> +/*
> + * smi_kthread_fn - Used to periodically sample the CPU TSC via smi_get_sample.
> + *                  We use stop_machine, which intentionally introduces latency.
> + */
> +
> +static int smi_kthread_fn(void *data)
> +{
> +	int err = 0;
> +	struct smdata_struct *smi_data = (struct smdata_struct *)data;

Unneeded cast of void*.

> +	while (!kthread_should_stop()) {
> +		err = stop_machine(smi_get_sample, smi_data, 0);
> +
> +		wake_up(&smi_data->wq);
> +
> +		if (msleep_interruptible(smi_interval_ms))
> +			goto out;

hm, how can this happen?  Can root kill the kernel thread?  I think
that gets ignored..

> +	}
> +
> +out:
> +	return 0;
> +}
> +
> +struct task_struct *start_smi_thread(void)
> +{
> +	return smi_kthread = kthread_run(smi_kthread_fn, &smdata,
> +					 "smi_detector");
> +}

All callers of this function ignore its return value.


> +void stop_smi_thread(void)
> +{
> +	if (smi_kthread)
> +		kthread_stop(smi_kthread);
> +}

This seems to assume that kthread_run() returns NULL on failure.  But
it returns an ERR_PTR.

> +static int smi_debug_sample_fopen(struct inode *inode, struct file *filp)
> +{
> +
> +	filp->private_data = (void *)&smdata;

unneeded cast.

> +	return 0;
> +}

missing newline.

> +static ssize_t smi_debug_sample_fread(struct file *filp, char __user *ubuf,
> +					size_t cnt, loff_t *ppos)
> +{
> +	int len;
> +	char buf[64];
> +	struct smdata_struct *smi_data = filp->private_data;
> +
> +	if (!enabled)
> +		return 0;
> +
> +	wait_event_interruptible(smi_data->wq, atomic_read(&smi_data->pending));
> +	atomic_set(&smi_data->pending, 0);

Is this code racy?  (I couldn't be bothered working it out, but it
smells racy ;))

> +	len = sprintf(buf, "%lld\n", smi_data->last_sample);

%llu would be more accurate.

> +	if (copy_to_user(ubuf, buf, len))
> +		return -EFAULT;

Perhaps the kernel should have an snprintf_to_user() utility.  Maybe it
already has and I forgot.

> +	return len;
> +}
> +
> +static const struct file_operations smi_sample_fops = {
> +	.open		= smi_debug_sample_fopen,
> +	.read		= smi_debug_sample_fread,
> +	.owner		= THIS_MODULE,
> +};
> +
> +static int smi_debug_enable_fopen(struct inode *inode, struct file *filp)
> +{
> +	return 0;
> +}
> +
> +
> +static ssize_t smi_debug_enable_fread(struct file *filp, char __user *ubuf,
> +				      size_t cnt, loff_t *ppos)
> +{
> +	char buffer[4];
> +
> +	if (!cnt || *ppos)
> +		return 0;
> +
> +	buffer[0] = enabled ? '1' : '0';
> +	buffer[1] = '\n';
> +	buffer[2] = '\0';

This is unneeded.

> +	if (copy_to_user(ubuf, buffer, 2))
> +		return -EFAULT;

another snprintf_to_user() user!

> +	return *ppos = 2;
> +}
> +
> +static ssize_t  smi_debug_enable_fwrite(struct file *file,
> +					const char __user *user_buffer,
> +					size_t user_size,
> +					loff_t *offset)
> +{
> +	char buffer[4];
> +	int copy_size = min(user_size, sizeof(buffer));
> +	long val;
> +
> +	if (copy_from_user(buffer, user_buffer, copy_size))
> +		return -EFAULT;
> +#if 1
> +	val = simple_strtol(buffer, NULL, 10);
> +#else
> +	if (strict_strtol(buffer, 10, &val))
> +		return -EINVAL;
> +#endif

strict_strtoul() is preferred.

> +	mutex_lock(&enable_mutex);
> +	if (val) {
> +		if (enabled)
> +			goto unlock;
> +		smi_init_stats();
> +		enabled = 1;
> +		start_smi_thread();
> +	} else {
> +		if (!enabled)
> +			goto unlock;
> +		enabled = 0;
> +		stop_smi_thread();
> +	}
> +unlock:
> +	mutex_unlock(&enable_mutex);
> +	printk(SMI_BANNER "smi_detector thread %s\n",
> +		enabled ? "started" : "stopped");
> +	return user_size;
> +}
> +
> +static const struct file_operations smi_enable_fops = {
> +	.open		= smi_debug_enable_fopen,
> +	.read		= smi_debug_enable_fread,
> +	.write		= smi_debug_enable_fwrite,
> +	.owner		= THIS_MODULE,
> +};
> +
> +/* debugfs_create_bool */
> +int smi_detector_init(void)
> +{
> +
> +	printk(KERN_INFO SMI_BANNER "version %s\n", smi_version);
> +
> +	smi_init_stats();
> +
> +	init_waitqueue_head(&smdata.wq);
> +	atomic_set(&smdata.pending, 0);

These could have been done at compile time.

> +	smi_debug_dir = debugfs_create_dir("smi_detector", NULL);
> +
> +	if (smi_debug_dir == NULL) {
> +		printk(KERN_INFO SMI_BANNER "debugfs not mounted!\n");
> +		return -1;
> +	}
> +
> +	smi_debug_sample_ms = debugfs_create_u32("ms_per_sample",
> +				0644, smi_debug_dir, &smi_sample_ms);
> +	smi_debug_interval_ms = debugfs_create_u32("ms_between_samples",
> +				0644, smi_debug_dir, &smi_interval_ms);
> +	smi_debug_max = debugfs_create_u64("max_sample_us",
> +				0644, smi_debug_dir, &smdata.max_sample);
> +	smi_debug_smi = debugfs_create_u64("smi_count",
> +				0644, smi_debug_dir, &smdata.smi_count);
> +	smi_debug_sample = debugfs_create_file("sample_us",
> +				0444, smi_debug_dir, &smdata, &smi_sample_fops);
> +	smi_debug_frequency_us = debugfs_create_u64("avg_smi_interval_us",
> +				0444, smi_debug_dir, &smdata.frequency);
> +	smi_debug_threshold = debugfs_create_u64("latency_threshold_us",
> +				0444, smi_debug_dir, &smdata.threshold);
> +
> +	smi_debug_enable = debugfs_create_file("enable",
> +				0644, smi_debug_dir,
> +				&enabled, &smi_enable_fops);
> +
> +
> +	if (enabled)
> +		start_smi_thread();
> +
> +	return 0;
> +}
> +
> +void smi_detector_exit(void)
> +{
> +	if (enabled) {
> +		mutex_lock(&enable_mutex);
> +		enabled = 0;
> +		stop_smi_thread();
> +		mutex_unlock(&enable_mutex);
> +	}
> +	if (smi_debug_sample_ms)
> +		debugfs_remove(smi_debug_sample_ms);
> +	if (smi_debug_interval_ms)
> +		debugfs_remove(smi_debug_interval_ms);
> +	if (smi_debug_max)
> +		debugfs_remove(smi_debug_max);
> +	if (smi_debug_smi)
> +		debugfs_remove(smi_debug_smi);
> +	if (smi_debug_frequency_us)
> +		debugfs_remove(smi_debug_frequency_us);
> +	if (smi_debug_threshold)
> +		debugfs_remove(smi_debug_threshold);
> +	if (smi_debug_sample)
> +		debugfs_remove(smi_debug_sample);
> +	if (smi_debug_enable)
> +		debugfs_remove(smi_debug_enable);
> +	if (smi_debug_dir)
> +		debugfs_remove(smi_debug_dir);

debugfs_remove(NULL) is legal, so all the if()s can be removed.

> +}
> +
> +module_init(smi_detector_init);
> +module_exit(smi_detector_exit);
> diff --git a/scripts/smidetect b/scripts/smidetect
> new file mode 100644
> index 0000000..81593a1
> --- /dev/null
> +++ b/scripts/smidetect
> @@ -0,0 +1,282 @@
> +#!/usr/bin/python

Some documentation here would be nice.  An overview of what it does,
command line options, pointer to the .txt file.

[PATCH 2/2] SMI detector: add license to the user smidetect script

[Jon Masters]

This adds a GPL v2. license to the smidetect script. That script is entirely
optional and can be used to make it easier to control the SMI detector from
within a python project.

Signed-off-by: Jon Masters <jcm@jonmasters.org>
---
 scripts/smidetect |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/scripts/smidetect b/scripts/smidetect
index 81593a1..a3ddcee 100644
--- a/scripts/smidetect
+++ b/scripts/smidetect
@@ -1,4 +1,12 @@
 #!/usr/bin/python
+#
+# A simple (optional) python script for interfacing with the smi_detector.
+# This script can be used to configure the smi_detector module, although
+# you can also simply use the debugfs file interface directly.
+#
+# Copyright (C) 2009 Clark Williams <williams@redhat.com>
+#
+# Licensed under the GNU General Public License, version 2.0.
 
 import sys
 import os
-- 
1.6.0.6