From: Valentin Schneider <vschneid@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-snps-arc@lists.infradead.org,
linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org,
linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org,
loongarch@lists.linux.dev, linux-mips@vger.kernel.org,
openrisc@lists.librecores.org, linux-parisc@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
linux-s390@vger.kernel.org, linux-sh@vger.kernel.org,
sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org,
x86@kernel.org, "Paul E. McKenney" <paulmck@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Juri Lelli <juri.lelli@redhat.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
Frederic Weisbecker <frederic@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>, Marc Zyngier <maz@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Russell King <linux@armlinux.org.uk>,
Nicholas Piggin <npiggin@gmail.com>, Guo Ren <guoren@kernel.org>,
"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH v5 7/7] sched, smp: Trace smp callback causing an IPI
Date: Thu, 23 Mar 2023 18:31:37 +0000 [thread overview]
Message-ID: <xhsmh8rfncoae.mognet@vschneid.remote.csb> (raw)
In-Reply-To: <20230323174129.GA2753619@hirez.programming.kicks-ass.net>
On 23/03/23 18:41, Peter Zijlstra wrote:
> On Thu, Mar 23, 2023 at 04:25:25PM +0000, Valentin Schneider wrote:
>> On 22/03/23 15:04, Peter Zijlstra wrote:
>> > @@ -798,14 +794,20 @@ static void smp_call_function_many_cond(
>> > }
>> >
>> > /*
>> > + * Trace each smp_function_call_*() as an IPI, actual IPIs
>> > + * will be traced with func==generic_smp_call_function_single_ipi().
>> > + */
>> > + trace_ipi_send_cpumask(cfd->cpumask_ipi, _RET_IP_, func);
>>
>> I just got a trace pointing out this can emit an event even though no IPI
>> is sent if e.g. the cond_func predicate filters all CPUs in the argument
>> mask:
>>
>> ipi_send_cpumask: cpumask= callsite=on_each_cpu_cond_mask+0x3c callback=flush_tlb_func+0x0
>>
>> Maybe something like so on top?
>>
>> ---
>> diff --git a/kernel/smp.c b/kernel/smp.c
>> index ba5478814e677..1dc452017d000 100644
>> --- a/kernel/smp.c
>> +++ b/kernel/smp.c
>> @@ -791,6 +791,8 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
>> }
>> }
>>
>> + if (!nr_cpus)
>> + goto local;
>
> Hmm, this isn't right. You can get nr_cpus==0 even though it did add
> some to various lists but never was first.
>
Duh, glanced over that.
> But urgh, even if we were to say count nr_queued we'd never get the mask
> right, because we don't track which CPUs have the predicate matched,
> only those we need to actually send an IPI to :/
>
> Ooh, I think we can clear those bits from cfd->cpumask, arguably that's
> a correctness fix too, because the 'run_remote && wait' case shouldn't
> wait on things we didn't queue.
>
Yeah, that makes sense to me. Just one tiny suggestion below.
> Hmm?
>
>
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -728,9 +728,9 @@ static void smp_call_function_many_cond(
> int cpu, last_cpu, this_cpu = smp_processor_id();
> struct call_function_data *cfd;
> bool wait = scf_flags & SCF_WAIT;
> + int nr_cpus = 0, nr_queued = 0;
> bool run_remote = false;
> bool run_local = false;
> - int nr_cpus = 0;
>
> lockdep_assert_preemption_disabled();
>
> @@ -772,8 +772,10 @@ static void smp_call_function_many_cond(
> for_each_cpu(cpu, cfd->cpumask) {
> call_single_data_t *csd = per_cpu_ptr(cfd->csd, cpu);
>
> - if (cond_func && !cond_func(cpu, info))
> + if (cond_func && !cond_func(cpu, info)) {
> + __cpumask_clear_cpu(cpu, cfd->cpumask);
> continue;
> + }
>
> csd_lock(csd);
> if (wait)
> @@ -789,13 +791,15 @@ static void smp_call_function_many_cond(
> nr_cpus++;
> last_cpu = cpu;
> }
> + nr_queued++;
> }
>
> /*
> * Trace each smp_function_call_*() as an IPI, actual IPIs
> * will be traced with func==generic_smp_call_function_single_ipi().
> */
> - trace_ipi_send_cpumask(cfd->cpumask_ipi, _RET_IP_, func);
> + if (nr_queued)
With your change to cfd->cpumask, we could ditch nr_queued and make this
if (!cpumask_empty(cfd->cpumask))
since cfd->cpumask now only contains CPUs that have had a CSD queued.
> + trace_ipi_send_cpumask(cfd->cpumask, _RET_IP_, func);
>
> /*
> * Choose the most efficient way to send an IPI. Note that the
_______________________________________________
linux-snps-arc mailing list
linux-snps-arc@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-snps-arc
prev parent reply other threads:[~2023-03-23 18:31 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-07 14:35 [PATCH v5 0/7] Generic IPI sending tracepoint Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 1/7] trace: Add trace_ipi_send_cpumask() Valentin Schneider
2023-03-22 9:39 ` Peter Zijlstra
2023-03-22 10:30 ` Peter Zijlstra
2023-03-22 11:24 ` Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 2/7] sched, smp: Trace IPIs sent via send_call_function_single_ipi() Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 3/7] smp: Trace IPIs sent via arch_send_call_function_ipi_mask() Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 4/7] irq_work: Trace self-IPIs sent via arch_irq_work_raise() Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 5/7] treewide: Trace IPIs sent via smp_send_reschedule() Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 6/7] smp: reword smp call IPI comment Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 7/7] sched, smp: Trace smp callback causing an IPI Valentin Schneider
2023-03-22 9:53 ` Peter Zijlstra
2023-03-22 12:20 ` Valentin Schneider
2023-03-22 14:04 ` Peter Zijlstra
2023-03-22 17:01 ` Valentin Schneider
2023-03-22 17:22 ` Peter Zijlstra
2023-03-22 18:22 ` Valentin Schneider
2023-03-22 23:14 ` Peter Zijlstra
2023-03-23 16:25 ` Valentin Schneider
2023-03-23 17:41 ` Peter Zijlstra
2023-03-23 18:31 ` Valentin Schneider [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=xhsmh8rfncoae.mognet@vschneid.remote.csb \
--to=vschneid@redhat.com \
--cc=bigeasy@linutronix.de \
--cc=bp@alien8.de \
--cc=bristot@redhat.com \
--cc=dave.hansen@linux.intel.com \
--cc=davem@davemloft.net \
--cc=frederic@kernel.org \
--cc=guoren@kernel.org \
--cc=hpa@zytor.com \
--cc=juri.lelli@redhat.com \
--cc=linux-alpha@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-csky@vger.kernel.org \
--cc=linux-hexagon@vger.kernel.org \
--cc=linux-ia64@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@vger.kernel.org \
--cc=linux-parisc@vger.kernel.org \
--cc=linux-riscv@lists.infradead.org \
--cc=linux-s390@vger.kernel.org \
--cc=linux-sh@vger.kernel.org \
--cc=linux-snps-arc@lists.infradead.org \
--cc=linux-xtensa@linux-xtensa.org \
--cc=linux@armlinux.org.uk \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=loongarch@lists.linux.dev \
--cc=mark.rutland@arm.com \
--cc=maz@kernel.org \
--cc=mingo@redhat.com \
--cc=mtosatti@redhat.com \
--cc=npiggin@gmail.com \
--cc=openrisc@lists.librecores.org \
--cc=paulmck@kernel.org \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=sparclinux@vger.kernel.org \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).