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

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Message-ID: <CAAuSN90CXXEdco_fNYrv-ZUZPr4nB4HYPM1NCgaSgGz+Z-jaRQ@mail.gmail.com>
Date:	Thu, 11 Aug 2011 13:31:13 -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 1:23 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, 2011-08-11 at 13:10 -0700, Alex Neronskiy wrote:
> Ah, right, yeah, stick another lock in there.. One does worry about the
> whole writer concurrency thing though, isn't it likely all cpus will
> tickle the thing in quick succession? Putting a global lock in that path
> isn't good,.. always think of the poor sod with the 4096 cpu machine.
Is it common to disable interrupts on all 4096 CPU's at once?

> Also, is all of this really useful? The hardlockup watchdog is useful
> when you mess up bad, but other than that I've never found it to be
> useful at all.
>
> 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.
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