From: Thomas Gleixner <tglx@linutronix.de>
To: Waiman Long <longman@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
Kees Cook <keescook@chromium.org>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Davidlohr Bueso <dave@stgolabs.net>,
Miklos Szeredi <miklos@szeredi.hu>,
Daniel Colascione <dancol@google.com>,
Dave Chinner <david@fromorbit.com>,
Randy Dunlap <rdunlap@infradead.org>,
Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH v3 4/4] /proc/stat: Call kstat_irqs_usr() only for active IRQs
Date: Fri, 11 Jan 2019 18:23:24 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.21.1901111750280.4957@nanos.tec.linutronix.de> (raw)
In-Reply-To: <1547061648-16080-5-git-send-email-longman@redhat.com>
On Wed, 9 Jan 2019, Waiman Long wrote:
> ---
> fs/proc/stat.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 84 insertions(+)
and the total diffstat of that patch series is:
4 files changed, 125 insertions(+), 12 deletions(-)
> static void show_stat_irqs(struct seq_file *p)
> @@ -100,9 +119,74 @@ static void show_stat_irqs(struct seq_file *p)
> int i;
>
> seq_put_decimal_ull(p, "intr ", compute_stat_irqs_sum());
> +
> + if (IS_ENABLED(CONFIG_SMP) && (nr_cpu_ids >= 10) && (nr_irqs >= 256)) {
> + /*
> + * On systems with 10 or more CPUs and 256 or more IRQs,
> + * we used a bitmap to keep track of the number of active
> + * IRQs and call kstat_irqs_usr() only for those IRQs.
> + * The bitmap will be refreshed whenever nr_active_irqs
> + * changes.
> + */
> + extern atomic_t nr_active_irqs;
> + static DEFINE_MUTEX(irqs_mutex);
> + static int last_irq = -1;
> + static int bitmap_size, active_irqs;
> + static unsigned long *bitmap;
> + int current_irqs = atomic_read(&nr_active_irqs);
This is completely overengineered. The simple patch below does not need
conditionals and atomics, is unconditional and completely avoids this
bitmap hackery.
On a VM with 144 VCPUs and nr_irqs=1576 and a loop of 5000 readouts of
/proc/stat (python):
Before After
real 0m1.331s 0m0.728s -45.3%
user 0m0.415s 0m0.359s -13.5%
sys 0m0.914s 0m0.356s -61.1%
Hmm?
Thanks,
tglx
8<------------------
fs/proc/stat.c | 28 +++++++++++++++++++++++++---
include/linux/irqdesc.h | 3 ++-
kernel/irq/internals.h | 1 +
kernel/irq/irqdesc.c | 7 ++-----
4 files changed, 30 insertions(+), 9 deletions(-)
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -79,6 +79,30 @@ static u64 get_iowait_time(int cpu)
#endif
+static void show_irq_gap(struct seq_file *p, int gap)
+{
+ static const char zeros[] = " 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0";
+
+ while (gap > 0) {
+ int inc = min_t(int, gap, ARRAY_SIZE(zeros) / 2);
+
+ seq_write(p, zeros, 2 * inc);
+ gap -= inc;
+ }
+}
+
+static void show_all_irqs(struct seq_file *p)
+{
+ int i, next = 0;
+
+ for_each_active_irq(i) {
+ show_irq_gap(p, i - next);
+ seq_put_decimal_ull(p, " ", kstat_irqs_usr(i));
+ next = i + 1;
+ }
+ show_irq_gap(p, nr_irqs - next);
+}
+
static int show_stat(struct seq_file *p, void *v)
{
int i, j;
@@ -156,9 +180,7 @@ static int show_stat(struct seq_file *p,
}
seq_put_decimal_ull(p, "intr ", (unsigned long long)sum);
- /* sum again ? it could be updated? */
- for_each_irq_nr(j)
- seq_put_decimal_ull(p, " ", kstat_irqs_usr(j));
+ show_all_irqs(p);
seq_printf(p,
"\nctxt %llu\n"
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -65,9 +65,10 @@ struct irq_desc {
unsigned int core_internal_state__do_not_mess_with_it;
unsigned int depth; /* nested irq disables */
unsigned int wake_depth; /* nested wake enables */
+ unsigned int tot_count;
unsigned int irq_count; /* For detecting broken IRQs */
- unsigned long last_unhandled; /* Aging timer for unhandled count */
unsigned int irqs_unhandled;
+ unsigned long last_unhandled; /* Aging timer for unhandled count */
atomic_t threads_handled;
int threads_handled_last;
raw_spinlock_t lock;
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -246,6 +246,7 @@ static inline void kstat_incr_irqs_this_
{
__this_cpu_inc(*desc->kstat_irqs);
__this_cpu_inc(kstat.irqs_sum);
+ desc->tot_count++;
}
static inline int irq_desc_get_node(struct irq_desc *desc)
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -119,6 +119,7 @@ static void desc_set_defaults(unsigned i
desc->depth = 1;
desc->irq_count = 0;
desc->irqs_unhandled = 0;
+ desc->tot_count = 0;
desc->name = NULL;
desc->owner = owner;
for_each_possible_cpu(cpu)
@@ -919,14 +920,10 @@ unsigned int kstat_irqs_cpu(unsigned int
unsigned int kstat_irqs(unsigned int irq)
{
struct irq_desc *desc = irq_to_desc(irq);
- int cpu;
- unsigned int sum = 0;
if (!desc || !desc->kstat_irqs)
return 0;
- for_each_possible_cpu(cpu)
- sum += *per_cpu_ptr(desc->kstat_irqs, cpu);
- return sum;
+ return desc->tot_count;
}
/**
next prev parent reply other threads:[~2019-01-11 17:23 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-09 19:20 [PATCH v3 0/4] /proc/stat: Reduce irqs counting performance overhead Waiman Long
2019-01-09 19:20 ` [PATCH v3 1/4] /proc/stat: Extract irqs counting code into show_stat_irqs() Waiman Long
2019-01-09 19:20 ` [PATCH v3 2/4] /proc/stat: Only do percpu sum of active IRQs Waiman Long
2019-01-09 19:20 ` [PATCH v3 3/4] genirq: Track the number " Waiman Long
2019-01-09 19:20 ` [PATCH v3 4/4] /proc/stat: Call kstat_irqs_usr() only for " Waiman Long
2019-01-11 17:23 ` Thomas Gleixner [this message]
2019-01-11 19:19 ` Thomas Gleixner
2019-01-11 19:23 ` Matthew Wilcox
2019-01-11 21:02 ` Thomas Gleixner
2019-01-14 19:04 ` Waiman Long
2019-01-15 9:24 ` Thomas Gleixner
2019-01-15 15:52 ` Waiman Long
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