From: Frederic Weisbecker <frederic@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
Yunfeng Ye <yeyunfeng@huawei.com>,
Frederic Weisbecker <frederic@kernel.org>,
Marcelo Tosatti <mtosatti@redhat.com>
Subject: [PATCH 01/10] tick/nohz: Evaluate the CPU expression after the static key
Date: Thu, 13 May 2021 01:29:15 +0200 [thread overview]
Message-ID: <20210512232924.150322-2-frederic@kernel.org> (raw)
In-Reply-To: <20210512232924.150322-1-frederic@kernel.org>
From: Peter Zijlstra <peterz@infradead.org>
When tick_nohz_full_cpu() is called with smp_processor_id(), the latter
is unconditionally evaluated whether the static key is on or off. It is
not necessary in the off-case though, so make sure the cpu expression
is executed at the last moment.
Illustrate with the following test function:
int tick_nohz_test(void)
{
return tick_nohz_full_cpu(smp_processor_id());
}
The resulting code before was:
mov %gs:0x7eea92d1(%rip),%eax # smp_processor_id() fetch
nopl 0x0(%rax,%rax,1)
xor %eax,%eax
retq
cmpb $0x0,0x29d393a(%rip) # <tick_nohz_full_running>
je tick_nohz_test+0x29 # jump to below eax clear
mov %eax,%eax
bt %rax,0x29d3936(%rip) # <tick_nohz_full_mask>
setb %al
movzbl %al,%eax
retq
xor %eax,%eax
retq
Now it becomes:
nopl 0x0(%rax,%rax,1)
xor %eax,%eax
retq
cmpb $0x0,0x29d3871(%rip) # <tick_nohz_full_running>
je tick_nohz_test+0x29 # jump to below eax clear
mov %gs:0x7eea91f0(%rip),%eax # smp_processor_id() fetch, after static key
mov %eax,%eax
bt %rax,0x29d3866(%rip) # <tick_nohz_full_mask>
setb %al
movzbl %al,%eax
retq
xor %eax,%eax
retq
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Yunfeng Ye <yeyunfeng@huawei.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
include/linux/tick.h | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)
diff --git a/include/linux/tick.h b/include/linux/tick.h
index 7340613c7eff..2258984a0e8a 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -185,13 +185,17 @@ static inline bool tick_nohz_full_enabled(void)
return tick_nohz_full_running;
}
-static inline bool tick_nohz_full_cpu(int cpu)
-{
- if (!tick_nohz_full_enabled())
- return false;
-
- return cpumask_test_cpu(cpu, tick_nohz_full_mask);
-}
+/*
+ * Check if a CPU is part of the nohz_full subset. Arrange for evaluating
+ * the cpu expression (typically smp_processor_id()) _after_ the static
+ * key.
+ */
+#define tick_nohz_full_cpu(_cpu) ({ \
+ bool __ret = false; \
+ if (tick_nohz_full_enabled()) \
+ __ret = cpumask_test_cpu((_cpu), tick_nohz_full_mask); \
+ __ret; \
+})
static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask)
{
--
2.25.1
next prev parent reply other threads:[~2021-05-12 23:43 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-12 23:29 [GIT PULL] tick/nohz updates v3 Frederic Weisbecker
2021-05-12 23:29 ` Frederic Weisbecker [this message]
2021-05-13 13:17 ` [tip: timers/nohz] tick/nohz: Evaluate the CPU expression after the static key tip-bot2 for Peter Zijlstra
2021-05-12 23:29 ` [PATCH 02/10] tick/nohz: Conditionally restart tick on idle exit Frederic Weisbecker
2021-05-13 13:17 ` [tip: timers/nohz] " tip-bot2 for Yunfeng Ye
2021-05-12 23:29 ` [PATCH 03/10] tick/nohz: Remove superflous check for CONFIG_VIRT_CPU_ACCOUNTING_NATIVE Frederic Weisbecker
2021-05-13 13:17 ` [tip: timers/nohz] " tip-bot2 for Frederic Weisbecker
2021-05-12 23:29 ` [PATCH 04/10] tick/nohz: Update idle_exittime on actual idle exit Frederic Weisbecker
2021-05-13 13:17 ` [tip: timers/nohz] " tip-bot2 for Yunfeng Ye
2021-05-12 23:29 ` [PATCH 05/10] tick/nohz: Update nohz_full Kconfig help Frederic Weisbecker
2021-05-13 13:17 ` [tip: timers/nohz] " tip-bot2 for Frederic Weisbecker
2021-05-12 23:29 ` [PATCH 06/10] tick/nohz: Only wakeup a single target cpu when kicking a task Frederic Weisbecker
2021-05-13 13:17 ` [tip: timers/nohz] tick/nohz: Only wake up " tip-bot2 for Frederic Weisbecker
2021-05-12 23:29 ` [PATCH 07/10] tick/nohz: Change signal tick dependency to wakeup CPUs of member tasks Frederic Weisbecker
2021-05-13 13:17 ` [tip: timers/nohz] tick/nohz: Change signal tick dependency to wake up " tip-bot2 for Marcelo Tosatti
2021-05-12 23:29 ` [PATCH 08/10] tick/nohz: Kick only _queued_ task whose tick dependency is updated Frederic Weisbecker
2021-05-13 13:17 ` [tip: timers/nohz] " tip-bot2 for Marcelo Tosatti
2021-05-12 23:29 ` [PATCH 09/10] tick/nohz: Call tick_nohz_task_switch() with interrupts disabled Frederic Weisbecker
2021-05-13 13:17 ` [tip: timers/nohz] " tip-bot2 for Peter Zijlstra
2021-05-12 23:29 ` [PATCH 10/10] MAINTAINERS: Add myself as context tracking maintainer Frederic Weisbecker
2021-05-19 9:21 ` [tip: timers/nohz] " tip-bot2 for Frederic Weisbecker
2021-05-13 12:23 ` [GIT PULL] tick/nohz updates v3 Ingo Molnar
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