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Message-ID: <1ab5082c-bec5-53f2-501b-f15f7e8edbd9@redhat.com>
Date: Fri, 18 Nov 2022 17:42:34 +0100
From: Daniel Bristot de Oliveira <bristot@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>,
Valentin Schneider <vschneid@...hat.com>
Cc: linux-alpha@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-snps-arc@...ts.infradead.org,
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x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Juri Lelli <juri.lelli@...hat.com>,
Marcelo Tosatti <mtosatti@...hat.com>,
Frederic Weisbecker <frederic@...nel.org>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>, Marc Zyngier <maz@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Russell King <linux@...linux.org.uk>,
Nicholas Piggin <npiggin@...il.com>,
Guo Ren <guoren@...nel.org>,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [RFC PATCH v2 8/8] sched, smp: Trace smp callback causing an IPI
On 11/18/22 10:12, Peter Zijlstra wrote:
> On Thu, Nov 17, 2022 at 02:45:29PM +0000, Valentin Schneider wrote:
>
>>> + if (trace_ipi_send_cpumask_enabled()) {
>>> + call_single_data_t *csd;
>>> + smp_call_func_t func;
>>> +
>>> + csd = container_of(node, call_single_data_t, node.llist);
>>> +
>>> + func = sched_ttwu_pending;
>>> + if (CSD_TYPE(csd) != CSD_TYPE_TTWU)
>>> + func = csd->func;
>>> +
>>> + if (raw_smp_call_single_queue(cpu, node))
>>> + trace_ipi_send_cpumask(cpumask_of(cpu), _RET_IP_, func);
>> So I went with the tracepoint being placed *before* the actual IPI gets
>> sent to have a somewhat sane ordering between trace_ipi_send_cpumask() and
>> e.g. trace_call_function_single_entry().
>>
>> Packaging the call_single_queue logic makes the code less horrible, but it
>> does mix up the event ordering...
> Keeps em sharp ;-)
>
Having the trace before the IPI avoids the (non ideal) case where the trace stops because of
an IPI execution before we have trace about who sent it... :-(.
-- Daniel
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