From: Thomas Gleixner <tglx@linutronix.de>
To: Shaohua Li <shli@fb.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
X86 ML <x86@kernel.org>,
Kernel-team@fb.com, "H. Peter Anvin" <hpa@zytor.com>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
John Stultz <john.stultz@linaro.org>
Subject: Re: [PATCH v2 3/3] X86: Add a thread cpu time implementation to vDSO
Date: Fri, 19 Dec 2014 01:34:56 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.11.1412190131500.17382@nanos> (raw)
In-Reply-To: <20141219003044.GA2804333@devbig257.prn2.facebook.com>
On Thu, 18 Dec 2014, Shaohua Li wrote:
> On Thu, Dec 18, 2014 at 04:22:59PM -0800, Andy Lutomirski wrote:
> > Bad news: this patch is incorrect, I think. Take a look at
> > update_rq_clock -- it does fancy things involving irq time and
> > paravirt steal time. So this patch could result in extremely
> > non-monotonic results.
>
> Yes, it's not precise. But bear in mind, CONFIG_IRQ_TIME_ACCOUNTING is a
> optional feature. Actually it's added not long time ago. I thought it's
> acceptable the time isn't precise just like what we have before the
> feature is added.
Wrong thought, really.
If the vdso can give you observable inconsistent representation
vs. real syscalls then it does not matter at all how long ago the
feature was added. It's simply wrong no matter what.
Thanks,
tglx
next prev parent reply other threads:[~2014-12-19 0:35 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-17 23:12 [PATCH v2 1/3] X86: make VDSO data support multiple pages Shaohua Li
2014-12-17 23:12 ` [PATCH v2 2/3] X86: add a generic API to let vdso code detect context switch Shaohua Li
2014-12-19 1:05 ` Thomas Gleixner
2014-12-17 23:12 ` [PATCH v2 3/3] X86: Add a thread cpu time implementation to vDSO Shaohua Li
2014-12-18 23:30 ` Andy Lutomirski
2014-12-19 0:22 ` Andy Lutomirski
2014-12-19 0:30 ` Shaohua Li
2014-12-19 0:32 ` Andy Lutomirski
2014-12-19 0:34 ` Thomas Gleixner [this message]
2014-12-19 11:23 ` Peter Zijlstra
2014-12-19 16:48 ` Andy Lutomirski
2014-12-19 17:03 ` Peter Zijlstra
2014-12-19 17:07 ` Andy Lutomirski
2014-12-19 17:27 ` Peter Zijlstra
2014-12-19 17:42 ` Andy Lutomirski
2015-01-02 2:59 ` Shaohua Li
2015-01-02 15:31 ` David Ahern
2015-01-02 17:02 ` Shaohua Li
2015-01-02 17:09 ` David Ahern
2015-01-02 17:17 ` Shaohua Li
2015-01-02 17:26 ` David Ahern
2015-01-02 17:47 ` Andy Lutomirski
2015-01-05 23:23 ` Shaohua Li
2015-01-06 10:18 ` Peter Zijlstra
2015-01-06 16:59 ` Shaohua Li
2015-01-12 19:50 ` Shaohua Li
2014-12-19 17:42 ` Chris Mason
2014-12-19 17:53 ` Andy Lutomirski
2014-12-19 18:16 ` Shaohua Li
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