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[2001:4c4e:1c86:4000:f9b8:756a:94f1:216]) by smtp.gmail.com with ESMTPSA id s2sm8795897ejn.112.2021.03.01.23.05.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Mar 2021 23:05:04 -0800 (PST) Sender: Ingo Molnar Date: Tue, 2 Mar 2021 08:05:02 +0100 From: Ingo Molnar To: Peter Zijlstra Cc: Nadav Amit , linux-kernel@vger.kernel.org, Andy Lutomirski , Thomas Gleixner , Nadav Amit , Dave Hansen , Rik van Riel , Josh Poimboeuf Subject: [PATCH] smp: Micro-optimize smp_call_function_many_cond() Message-ID: <20210302070502.GA2809110@gmail.com> References: <20210220231712.2475218-1-namit@vmware.com> <20210220231712.2475218-2-namit@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Peter Zijlstra 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 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 Signed-off-by: Ingo Molnar 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); }