From: Ingo Molnar <mingo@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Nadav Amit <nadav.amit@gmail.com>,
linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Nadav Amit <namit@vmware.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Rik van Riel <riel@surriel.com>,
Josh Poimboeuf <jpoimboe@redhat.com>
Subject: [PATCH] smp: Micro-optimize smp_call_function_many_cond()
Date: Tue, 2 Mar 2021 08:05:02 +0100 [thread overview]
Message-ID: <20210302070502.GA2809110@gmail.com> (raw)
In-Reply-To: <YD0gF9VuqKyVUgVS@hirez.programming.kicks-ass.net>
* Peter Zijlstra <peterz@infradead.org> wrote:
> On Sat, Feb 20, 2021 at 03:17:04PM -0800, Nadav Amit wrote:
> > + /*
> > + * Choose the most efficient way to send an IPI. Note that the
> > + * number of CPUs might be zero due to concurrent changes to the
> > + * provided mask.
> > + */
> > + if (nr_cpus == 1)
> > + arch_send_call_function_single_ipi(last_cpu);
> > + else if (likely(nr_cpus > 1))
> > + arch_send_call_function_ipi_mask(cfd->cpumask_ipi);
>
> I just ran into conflicts with another patch set, and noticed that the
> above should probably be:
>
> if (nr_cpus == 1)
> send_call_function_single_ipi(last_cpu);
> else if (likely(nr_cpus > 1))
> arch_send_call_function_ipi_mask(cfd->cpumask_ipi);
>
> Which will avoid the IPI when @last_cpu is idle.
I turned this into the additional patch below, on top of Nadav's series.
Thanks,
Ingo
===============>
From: Ingo Molnar <mingo@kernel.org>
Date: Tue, 2 Mar 2021 08:02:43 +0100
Subject: [PATCH] smp: Micro-optimize smp_call_function_many_cond()
Call the generic send_call_function_single_ipi() function, which
will avoid the IPI when @last_cpu is idle.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org
---
kernel/smp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/smp.c b/kernel/smp.c
index b6375d775e93..af0d51da84a2 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -694,7 +694,7 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
* provided mask.
*/
if (nr_cpus == 1)
- arch_send_call_function_single_ipi(last_cpu);
+ send_call_function_single_ipi(last_cpu);
else if (likely(nr_cpus > 1))
arch_send_call_function_ipi_mask(cfd->cpumask_ipi);
}
next prev parent reply other threads:[~2021-03-02 8:28 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-20 23:17 [PATCH v6 0/9] x86/tlb: Concurrent TLB flushes Nadav Amit
2021-02-20 23:17 ` [PATCH v6 1/9] smp: Run functions concurrently in smp_call_function_many_cond() Nadav Amit
2021-03-01 17:10 ` Peter Zijlstra
2021-03-01 19:01 ` Nadav Amit
2021-03-02 7:05 ` Ingo Molnar [this message]
2021-03-02 9:54 ` [tip: x86/mm] " tip-bot2 for Nadav Amit
2021-03-06 12:12 ` tip-bot2 for Nadav Amit
2021-02-20 23:17 ` [PATCH v6 2/9] x86/mm/tlb: Unify flush_tlb_func_local() and flush_tlb_func_remote() Nadav Amit
2021-03-02 9:54 ` [tip: x86/mm] " tip-bot2 for Nadav Amit
2021-03-06 12:12 ` tip-bot2 for Nadav Amit
2021-02-20 23:17 ` [PATCH v6 3/9] x86/mm/tlb: Open-code on_each_cpu_cond_mask() for tlb_is_not_lazy() Nadav Amit
2021-03-02 9:54 ` [tip: x86/mm] " tip-bot2 for Nadav Amit
2021-03-06 12:12 ` tip-bot2 for Nadav Amit
2021-02-20 23:17 ` [PATCH v6 4/9] x86/mm/tlb: Flush remote and local TLBs concurrently Nadav Amit
2021-03-02 9:54 ` [tip: x86/mm] " tip-bot2 for Nadav Amit
2021-03-06 12:12 ` tip-bot2 for Nadav Amit
2021-02-20 23:17 ` [PATCH v6 5/9] x86/mm/tlb: Privatize cpu_tlbstate Nadav Amit
2021-03-02 9:54 ` [tip: x86/mm] " tip-bot2 for Nadav Amit
2021-03-06 12:12 ` tip-bot2 for Nadav Amit
2021-02-20 23:17 ` [PATCH v6 6/9] x86/mm/tlb: Do not make is_lazy dirty for no reason Nadav Amit
2021-03-02 9:54 ` [tip: x86/mm] " tip-bot2 for Nadav Amit
2021-03-06 12:12 ` tip-bot2 for Nadav Amit
2021-02-20 23:17 ` [PATCH v6 7/9] cpumask: Mark functions as pure Nadav Amit
2021-03-02 9:54 ` [tip: x86/mm] " tip-bot2 for Nadav Amit
2021-03-06 12:12 ` tip-bot2 for Nadav Amit
2021-02-20 23:17 ` [PATCH v6 8/9] x86/mm/tlb: Remove unnecessary uses of the inline keyword Nadav Amit
2021-03-02 9:54 ` [tip: x86/mm] " tip-bot2 for Nadav Amit
2021-03-06 12:12 ` tip-bot2 for Nadav Amit
2021-02-20 23:17 ` [PATCH v6 9/9] smp: inline on_each_cpu_cond() and on_each_cpu() Nadav Amit
2021-03-02 9:54 ` [tip: x86/mm] smp: Inline " tip-bot2 for Nadav Amit
2021-03-06 12:12 ` tip-bot2 for Nadav Amit
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