From: Thomas Renninger <trenn@suse.de>
To: Ming Lei <tom.leiming@gmail.com>
Cc: rostedt@goodmis.org, fweisbec@gmail.com,
jean.pihet@newoldbits.com, mingo@redhat.com,
linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org,
Len Brown <lenb@kernel.org>
Subject: Re: [PATCH 3/3] trace points: power: remove 'cpu_id' from trace_cpu_idle
Date: Mon, 22 Aug 2011 10:27:34 +0200 [thread overview]
Message-ID: <201108221027.34441.trenn@suse.de> (raw)
In-Reply-To: <CACVXFVPeFyg7YoAsY63Mpy9HVR1y3ibg9R8HnUfLVe=hKf3ApA@mail.gmail.com>
On Saturday, August 20, 2011 04:40:09 AM Ming Lei wrote:
> Hi,
>
> 2011/8/20 Thomas Renninger <trenn@suse.de>:
> > On Friday, August 19, 2011 05:04:04 PM tom.leiming@gmail.com wrote:
> >> From: Ming Lei <tom.leiming@gmail.com>
> >>
> >> This patch removes the 'cpu_id' parameter of the cpu_idle
> >> trace point, based on the ideas below:
> >>
> >> - the cpu_id which is passed to trace point is always the current
> >> cpu
> > Are you sure this will always be true?
>
> It is sure at least now, the only place to pass 'dev->cpu' is inside
> cpuidle_idle_call,
It was known that cpu_id is always the current cpu with current
implementation when this got introduced.
But the perf events API must not change back and forth for userspace
compatibility. Therefore the cpu_id was added in case
that future implementations want to pass info where the current cpu
is not the cpu which is sent to the sleep state.
> smp_processor_id() can't be used safely in preemptible context.
I expect the only side effect that could happen is that if smp_process_id
is interrupted you get the wrong core id on a cpu idle trace event.
This only happens if cpuidle is not used and even then should happen
very rarely, nothing to worry for a debug tool like that.
And it should get fixed if these idle functions get fully integrated into
cpuidle at some point of time.
Thomas
next prev parent reply other threads:[~2011-08-22 8:27 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-19 15:04 [PATCH 1/3] trace points: power: remove 'cpu_id' from trace_clock_* tom.leiming
2011-08-19 15:04 ` [PATCH 2/3] trace points: power: remove 'cpu_id' from trace_power_domain_target tom.leiming
2011-08-19 15:04 ` [PATCH 3/3] trace points: power: remove 'cpu_id' from trace_cpu_idle tom.leiming
2011-08-19 20:31 ` Thomas Renninger
2011-08-20 2:40 ` Ming Lei
2011-08-20 2:40 ` Ming Lei
2011-08-22 8:27 ` Thomas Renninger [this message]
2011-09-02 7:26 ` Jean Pihet
2011-09-02 7:38 ` Ming Lei
2011-08-19 15:14 ` [PATCH 1/3] trace points: power: remove 'cpu_id' from trace_clock_* Steven Rostedt
2011-08-19 15:39 ` Ming Lei
2011-08-19 16:16 ` Arjan van de Ven
2011-08-20 2:44 ` Ming Lei
2011-08-20 2:44 ` Ming Lei
2011-08-20 15:59 ` Arjan van de Ven
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