From: Borislav Petkov <bp@suse.de>
To: Feng Tang <feng.tang@intel.com>
Cc: "Luck, Tony" <tony.luck@intel.com>,
kernel test robot <rong.a.chen@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
lkp@lists.01.org, Mel Gorman <mgorman@suse.com>
Subject: Re: [LKP] Re: [x86/mce] 1de08dccd3: will-it-scale.per_process_ops -14.1% regression
Date: Mon, 24 Aug 2020 17:14:25 +0200 [thread overview]
Message-ID: <20200824151425.GF4794@zn.tnic> (raw)
In-Reply-To: <20200821020259.GA90000@shbuild999.sh.intel.com>
On Fri, Aug 21, 2020 at 10:02:59AM +0800, Feng Tang wrote:
> 1de08dccd383 x86/mce: Add a struct mce.kflags field
> 9554bfe403bd x86/mce: Convert the CEC to use the MCE notifier
>
> And strange thing is after using gcc9 and debian10 rootfs, with same commits
> the regression turns to a improvement,
How so?
> though the trend keeps, that if we
> changes the kflags from __u64 to __u32, the performance will be no change.
>
> Following is the comparing of regression, I also attached the perf-profile
> for old and new commit (let me know if you need more data)
>
>
> 9554bfe403bdfc08 1de08dccd383482a3e88845d355
> ---------------- ---------------------------
> %stddev %change %stddev
> \ | \
> 192362 -15.1% 163343 will-it-scale.287.processes
> 0.91 +0.2% 0.92 will-it-scale.287.processes_idle
> 669.67 -15.1% 568.50 will-it-scale.per_process_ops
This is the data from your previous measurement:
9554bfe403bdfc08 1de08dccd383482a3e88845d355
---------------- ---------------------------
%stddev %change %stddev
\ | \
668.00 -14.1% 573.75 will-it-scale.per_process_ops
If I'm reading it correctly, commit
1de08dccd383 ("x86/mce: Add a struct mce.kflags field")
is still the slower one vs
9554bfe403bd ("x86/mce: Convert the CEC to use the MCE notifier")
Or am I misreading it?
In any case, this really looks like what Tony said: this enlargement of
struct mce pushes some variable into a cacheline-misaligned placement,
causing it to bounce.
The $ 10^6 question is, which variable is that...
--
Regards/Gruss,
Boris.
SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 36809, AG Nürnberg
next prev parent reply other threads:[~2020-08-24 15:15 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-25 11:44 [x86/mce] 1de08dccd3: will-it-scale.per_process_ops -14.1% regression kernel test robot
2020-04-25 13:01 ` Borislav Petkov
2020-08-18 8:29 ` [LKP] " Feng Tang
2020-08-18 20:06 ` Luck, Tony
2020-08-19 2:04 ` Feng Tang
2020-08-19 2:23 ` Luck, Tony
2020-08-19 3:04 ` Feng Tang
2020-08-19 3:15 ` Feng Tang
2020-08-21 2:02 ` Feng Tang
2020-08-24 15:14 ` Borislav Petkov [this message]
2020-08-24 15:33 ` Feng Tang
2020-08-24 15:38 ` Luck, Tony
2020-08-24 15:48 ` Feng Tang
2020-08-24 16:12 ` Borislav Petkov
2020-08-24 16:56 ` Mel Gorman
2020-08-25 6:49 ` Feng Tang
2020-08-25 6:23 ` Feng Tang
2020-08-25 16:44 ` Luck, Tony
2020-08-26 1:45 ` Feng Tang
2020-08-28 17:48 ` Borislav Petkov
2020-08-31 2:16 ` Feng Tang
2020-08-31 7:56 ` Mel Gorman
2020-08-31 8:23 ` Feng Tang
2020-08-31 8:55 ` Mel Gorman
2020-08-31 12:53 ` Feng Tang
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