linux-kernel - Re: [PATCH 1/1] mm:improve the performance during fork

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Date:   Wed, 23 Dec 2020 09:46:17 +0800
From:   jun qian <qianjun.kernel@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] mm:improve the performance during fork

David Laight <David.Laight@...lab.com> 于2020年12月23日周三 上午2:42写道：
>
> 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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