linux-kernel - Re: [LKP] [cpuidle] 259231a045: will-it-scale.per_process

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Date:   Fri, 3 Jan 2020 10:36:14 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     Feng Tang <feng.tang@...el.com>
Cc:     kernel test robot <rong.a.chen@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>, lkp@...org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [LKP] [cpuidle] 259231a045: will-it-scale.per_process_ops -12.6%
 regression

Hi Feng,

On Fri, Jan 03, 2020 at 10:31:17AM +0800, Feng Tang wrote:
> On Tue, Dec 31, 2019 at 01:59:23PM +0800, Feng Tang wrote:
> > Hi Marcelo,
> > 
> > On Wed, Sep 18, 2019 at 10:13:34AM +0800, kernel test robot wrote:
> > > Greeting,
> > > 
> > > FYI, we noticed a -12.6% regression of will-it-scale.per_process_ops due to commit:
> > > 
> > > 
> > > commit: 259231a045616c4101d023a8f4dcc8379af265a6 ("cpuidle: add poll_limit_ns to cpuidle_device structure")
> > > https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next.git master
> > 
> > Any comments on this? We re-run the test for 5.5-rc1, and the regression remains.
> 
> Anyway, I found commit 259231a04 lost one "break" when moving
> the original code, thus the semantics is changed to the last
> enabled state's target_residency instead of the first enabled
> one's.
> 
> I don't know if it's intentional, and I guess no, so here 
> is a fix patch, please review, thanks

Not intentional.

> But even with this patch, the regression is still not recovered.
> 
> - Feng

This has been fixed upstream already, should be on Rafael's GIT tree.

> >From cddd6b409e18ce97a8d7b851db4400396f71d857 Mon Sep 17 00:00:00 2001
> From: Feng Tang <feng.tang@...el.com>
> Date: Thu, 2 Jan 2020 16:58:31 +0800
> Subject: [PATCH] cpuidle: Add back the lost break in cpuidle_poll_time
> 
> Commit c4cbb8b649b5 move the poll time calculation into a
> new function cpuidle_poll_time(), during which one "break"
> get lost, and the semantic is changed from the last enabled
> state's target_residency instead of the first enabled one's.
> 
> So add it back.
> 
> Fixes: c4cbb8b649b5 "cpuidle: add poll_limit_ns to cpuidle_device structure"
> Signed-off-by: Feng Tang <feng.tang@...el.com>
> Cc: Marcelo Tosatti <mtosatti@...hat.com>
> ---
>  drivers/cpuidle/cpuidle.c | 1 +
>  1 file changed, 1 insertion(+)

About the regression... if you only revert the 

drivers/cpuidle/poll_state.c

changes from 

259231a045616c4101d023a8f4dcc8379af265a6

Is the performance regression gone?