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From:   jun qian <qianjun.kernel@gmail.com>
Date:   Wed, 23 Dec 2020 09:46:17 +0800
Message-ID: <CAKc596Jsmp_EoeC5tT+YcOutJR7O5Pqmsc=96C-EFDY5b5mePQ@mail.gmail.com>
Subject: Re: [PATCH 1/1] mm:improve the performance during fork
To:     David Laight <David.Laight@aculab.com>
Cc:     "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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David Laight <David.Laight@aculab.com> =E4=BA=8E2020=E5=B9=B412=E6=9C=8823=
=E6=97=A5=E5=91=A8=E4=B8=89 =E4=B8=8A=E5=8D=882:42=E5=86=99=E9=81=93=EF=BC=
=9A
>
> From: qianjun
> > Sent: 22 December 2020 12:19
> >
> > In our project, Many business delays come from fork, so
> > we started looking for the reason why fork is time-consuming.
> > I used the ftrace with function_graph to trace the fork, found
> > that the vm_normal_page will be called tens of thousands and
> > the execution time of this vm_normal_page function is only a
> > few nanoseconds. And the vm_normal_page is not a inline function.
> > So I think if the function is inline style, it maybe reduce the
> > call time overhead.
>
> Beware of taking timings from ftrace function trace.
> The cost of the tracing is significant.
>
> You can get sensible numbers if you only trace very specific
> functions.
> Slightly annoyingly the output format changes if you enable
> the function exit trace - useful for the timestamp.
> ISTR it is possible to get the process id traced if you fiddle
> with enough options.
>
>         David
>

Thanks for your time

I have closed the ftrace when the test program is running. So the time
diff is without the
ftrace interference.And what does ISTR stand for :)  thanks.

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