linux-kernel - Re: [LKP] [x86_64,entry] f04e05b81e4: -62.7% time.user

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Date:	Thu, 6 Nov 2014 22:26:23 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	LKP <lkp@...org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Yuanhan Liu <yuanhan.liu@...ux.intel.com>
Subject: Re: [LKP] [x86_64,entry] f04e05b81e4: -62.7% time.user_time

On Thu, Nov 6, 2014 at 10:00 PM, LKP <lkp@...org> wrote:
> FYI, we noticed the below changes on
>
> git://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git x86/entry
> commit f04e05b81e4d9ae88bee379f12176f551a24394a ("x86_64,entry: Use sysret to return to userspace when possible")
>
>
> f2ee9bebb99dd4a4  f04e05b81e4d9ae88bee379f12  testbox/testcase/testparams
> ----------------  --------------------------
>          %stddev     %change         %stddev
>              \          |                \
>      24.09 ±  4%     -62.7%       8.99 ±  3%  lkp-wsx02/aim9/performance-300s-creat-clo
>      24.09           -62.7%       8.99        GEO-MEAN time.user_time
>

I don't really know how to interpret this.  Is this a good thing or a bad thing?

I actually expect this change to be a dramatic speedup for some
workloads.  Any chance you can send me the .config, kernel command
line, and whether you have any tracing features enabled?

--Andy
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