linux-kernel - Re: [PATCH v6 2/2] Output stall data in debugfs

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Message-ID: <CAAuSN916+7=Z-eFGRVMUydni=ougtFX_uvy6LXSUCPR0RtkcJQ@mail.gmail.com>
Date:	Thu, 11 Aug 2011 15:02:32 -0700
From:	Alex Neronskiy <zakmagnus@...omium.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Don Zickus <dzickus@...hat.com>,
	Mandeep Singh Baines <msb@...omium.org>
Subject: Re: [PATCH v6 2/2] Output stall data in debugfs

On Thu, Aug 11, 2011 at 2:17 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, 2011-08-11 at 13:31 -0700, Alex Neronskiy wrote:
>>
>> > I mean, we're at the point where a PREEMPT=y kernel has a pretty decent
>> > latency and the PREEMPT_RT kernels live at ~30us. So wth are you
>> > measuring?
>> Well, not all kernels have PREEMPT. Chromebook kernels don't, for example.
>
> Can one infer from that statement that the purpose is trying to measure
> non preempt latency? Why not use the tracer build for that purpose?
>
> Still the watchdog ticks at 1s intervals or so, anything that takes that
> long, even on voluntary preemption kernels is quite insane.
I think Don grasped the sentiment well about a month ago when he
commented on the first version of the patch, so I'll just resend his
words:
On Wed, Jul 13, 2011 at 6:43 AM, Don Zickus <dzickus@...hat.com> wrote:
> I like the idea of this patch.  It definitely helps with better statistics
> when trying to set the appropriate values for a soft/hard lockup as
> opposed to pulling numbers from the air.
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