[PATCH RFC] x86 / CPU: Add cpu isolation flag for avoiding disturbance from aperfmperf IPI

* [PATCH RFC] x86 / CPU: Add cpu isolation flag for avoiding disturbance from aperfmperf IPI
@ 2019-04-25 10:46 Konstantin Khlebnikov
  2019-04-25 11:45 ` Peter Zijlstra
  0 siblings, 1 reply; 4+ messages in thread
From: Konstantin Khlebnikov @ 2019-04-25 10:46 UTC (permalink / raw)
  To: Peter Zijlstra, linux-kernel
  Cc: Len Brown, Frederic Weisbecker, Rafael J. Wysocki, Ingo Molnar,
	Thomas Gleixner, Paul E. McKenney

Sensitive workloads like DPDK polling do not like any interrupts.

This patch adds flag 'freq' for boot option 'isolcpu': isolcpu=freq,<cpus>.

Users like show_cpuinfo() fallback to frequency from generic cpufreq
policy if arch-specific requesting method returns 0.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
 Documentation/admin-guide/kernel-parameters.txt |    3 +++
 arch/x86/kernel/cpu/aperfmperf.c                |   12 +++++++++++-
 include/linux/sched/isolation.h                 |    1 +
 kernel/sched/isolation.c                        |    6 ++++++
 4 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2b8ee90bb644..3797cd5c2b2e 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1900,6 +1900,9 @@
 			  <cpu number> begins at 0 and the maximum value is
 			  "number of CPUs in system - 1".
 
+			freq
+			  Do not request current cpu frequency via IPI.
+
 			The format of <cpu-list> is described above.
 
 
diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
index 804c49493938..e8fb917980a8 100644
--- a/arch/x86/kernel/cpu/aperfmperf.c
+++ b/arch/x86/kernel/cpu/aperfmperf.c
@@ -14,6 +14,7 @@
 #include <linux/percpu.h>
 #include <linux/cpufreq.h>
 #include <linux/smp.h>
+#include <linux/sched/isolation.h>
 
 #include "cpu.h"
 
@@ -86,6 +87,9 @@ unsigned int aperfmperf_get_khz(int cpu)
 	if (!static_cpu_has(X86_FEATURE_APERFMPERF))
 		return 0;
 
+	if (!housekeeping_cpu(cpu, HK_FLAG_FREQ))
+		return 0;
+
 	aperfmperf_snapshot_cpu(cpu, ktime_get(), true);
 	return per_cpu(samples.khz, cpu);
 }
@@ -102,9 +106,12 @@ void arch_freq_prepare_all(void)
 	if (!static_cpu_has(X86_FEATURE_APERFMPERF))
 		return;
 
-	for_each_online_cpu(cpu)
+	for_each_online_cpu(cpu) {
+		if (!housekeeping_cpu(cpu, HK_FLAG_FREQ))
+			continue;
 		if (!aperfmperf_snapshot_cpu(cpu, now, false))
 			wait = true;
+	}
 
 	if (wait)
 		msleep(APERFMPERF_REFRESH_DELAY_MS);
@@ -118,6 +125,9 @@ unsigned int arch_freq_get_on_cpu(int cpu)
 	if (!static_cpu_has(X86_FEATURE_APERFMPERF))
 		return 0;
 
+	if (!housekeeping_cpu(cpu, HK_FLAG_FREQ))
+		return 0;
+
 	if (aperfmperf_snapshot_cpu(cpu, ktime_get(), true))
 		return per_cpu(samples.khz, cpu);
 
diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index b0fb1446fe04..88e6013ac8a9 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -13,6 +13,7 @@ enum hk_flags {
 	HK_FLAG_TICK		= (1 << 4),
 	HK_FLAG_DOMAIN		= (1 << 5),
 	HK_FLAG_WQ		= (1 << 6),
+	HK_FLAG_FREQ		= (1 << 7),
 };
 
 #ifdef CONFIG_CPU_ISOLATION
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index b02d148e7672..456b5f1dfa11 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -140,6 +140,12 @@ static int __init housekeeping_isolcpus_setup(char *str)
 			continue;
 		}
 
+		if (!strncmp(str, "freq,", 5)) {
+			str += 5;
+			flags |= HK_FLAG_FREQ;
+			continue;
+		}
+
 		pr_warn("isolcpus: Error, unknown flag\n");
 		return 0;
 	}


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