From: Peter Zijlstra <peterz@infradead.org>
To: Venkatesh Pallipadi <venki@google.com>
Cc: Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Balbir Singh <balbir@linux.vnet.ibm.com>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
linux-kernel@vger.kernel.org, Paul Turner <pjt@google.com>
Subject: Re: [PATCH 2/6] Add IRQ_TIME_ACCOUNTING, finer accounting of CPU irq time
Date: Mon, 20 Sep 2010 19:23:12 +0200 [thread overview]
Message-ID: <1285003392.2275.755.camel@laptop> (raw)
In-Reply-To: <AANLkTinu+2N7xnkuzMvhL+3V=vbRMDNT6ep-OHPrbT4y@mail.gmail.com>
On Mon, 2010-09-20 at 10:13 -0700, Venkatesh Pallipadi wrote:
> >> + local_irq_save(flags);
> >> +
> >> + cpu = task_cpu(tsk);
> >
> > Can this ever be anything other can smp_processor_id() and current?
> >
> >> + now = sched_clock();
> >
> > this should be using one of the kernel/sched_clock.c thingies, probably
> > local_clock(), or sched_clock_cpu(cpu).
>
> I don't really need task there. I can use smp_processor_id() or
> task_cpu(tsk) and I think latter one would be cheaper.
Not sure, task_cpu() gets the cpu number from the task_info struct,
smp_processor_id() gets it from per-cpu storage, both are a single
memory read.
But I think its a tad confusing that this function has a task argument
at all, but if its always current, it would be slightly better to call
it 'curr' or something.
Also, local_irq_safe() followed by smp_processor_id() is clearly local,
task_cpu(tsk) can be anything.
> You mean sched_clock() is not the right interface to use here.
> sched_clock_cpu() uses either sched_clock or remote_cpu stuff which I
> don't really need here and local_clock() also has irq
> disable/smp_processor_id() and calls sched_clock_cpu in turn.
> sched_clock() seemed to be more appropriate.
yeah, use sched_clock_cpu(smp_processor_id()), sched_clock() can be
utter crap on x86, the code in kernel/sched_clock.c tries its best to
sanitize the crap we get from the hardware.
next prev parent reply other threads:[~2010-09-20 17:23 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-17 1:56 [PATCH 0/6] Proper kernel irq time accounting Venkatesh Pallipadi
2010-09-17 1:56 ` [PATCH 1/6] Consolidate account_system_vtime extern declaration Venkatesh Pallipadi
2010-09-17 1:56 ` [PATCH 2/6] Add IRQ_TIME_ACCOUNTING, finer accounting of CPU irq time Venkatesh Pallipadi
2010-09-19 11:11 ` Peter Zijlstra
2010-09-20 17:13 ` Venkatesh Pallipadi
2010-09-20 17:23 ` Peter Zijlstra [this message]
2010-09-19 11:21 ` Peter Zijlstra
2010-09-19 11:42 ` Peter Zijlstra
2010-09-19 12:01 ` Peter Zijlstra
2010-09-20 7:27 ` Martin Schwidefsky
2010-09-20 9:27 ` Peter Zijlstra
2010-09-20 17:16 ` Venkatesh Pallipadi
2010-09-20 17:26 ` Peter Zijlstra
2010-09-27 20:35 ` [PATCH] si time accounting accounts bh_disable'd time to si Venkatesh Pallipadi
2010-09-27 20:53 ` Eric Dumazet
2010-09-27 21:11 ` Venkatesh Pallipadi
2010-09-27 21:16 ` Eric Dumazet
2010-09-30 11:17 ` Peter Zijlstra
2010-09-17 1:56 ` [PATCH 3/6] x86: Add IRQ_TIME_ACCOUNTING in x86 Venkatesh Pallipadi
2010-09-17 1:56 ` [PATCH 4/6] sched: Do not account irq time to current task Venkatesh Pallipadi
2010-09-19 11:28 ` Peter Zijlstra
2010-09-20 17:33 ` Venkatesh Pallipadi
2010-09-20 17:38 ` Peter Zijlstra
2010-09-20 17:40 ` Venkatesh Pallipadi
2010-09-17 1:56 ` [PATCH 5/6] sched: Remove irq time from available CPU power Venkatesh Pallipadi
2010-09-19 11:31 ` Peter Zijlstra
2010-09-20 17:38 ` Venkatesh Pallipadi
2010-09-17 1:56 ` [PATCH 6/6] Export per cpu hardirq and softirq time in proc Venkatesh Pallipadi
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