49 lines
2.0 KiB
Diff
49 lines
2.0 KiB
Diff
From b842642f2c9c33d6d0430314326f0f0df15ac0a3 Mon Sep 17 00:00:00 2001
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Message-Id: <b842642f2c9c33d6d0430314326f0f0df15ac0a3.1601675153.git.zanussi@kernel.org>
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In-Reply-To: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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References: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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From: Waiman Long <longman@redhat.com>
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Date: Thu, 3 Oct 2019 16:36:08 -0400
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Subject: [PATCH 302/333] lib/smp_processor_id: Don't use cpumask_equal()
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.148-rt64.tar.xz
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[ Upstream commit 659252061477862f45b79e1de169e6030f5c8918 ]
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The check_preemption_disabled() function uses cpumask_equal() to see
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if the task is bounded to the current CPU only. cpumask_equal() calls
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memcmp() to do the comparison. As x86 doesn't have __HAVE_ARCH_MEMCMP,
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the slow memcmp() function in lib/string.c is used.
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On a RT kernel that call check_preemption_disabled() very frequently,
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below is the perf-record output of a certain microbenchmark:
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42.75% 2.45% testpmd [kernel.kallsyms] [k] check_preemption_disabled
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40.01% 39.97% testpmd [kernel.kallsyms] [k] memcmp
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We should avoid calling memcmp() in performance critical path. So the
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cpumask_equal() call is now replaced with an equivalent simpler check.
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Signed-off-by: Waiman Long <longman@redhat.com>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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---
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lib/smp_processor_id.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c
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index fb35c45b9421..b8a8a8db2d75 100644
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--- a/lib/smp_processor_id.c
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+++ b/lib/smp_processor_id.c
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@@ -22,7 +22,7 @@ notrace static unsigned int check_preemption_disabled(const char *what1,
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* Kernel threads bound to a single CPU can safely use
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* smp_processor_id():
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*/
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- if (cpumask_equal(current->cpus_ptr, cpumask_of(this_cpu)))
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+ if (current->nr_cpus_allowed == 1)
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goto out;
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/*
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--
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2.17.1
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