From: Stefan Wahren <stefan.wahren@i2se.com>
To: paulmck@kernel.org, Phil Elwell <phil@raspberrypi.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Nicolas Saenz Julienne <nsaenzju@redhat.com>,
Borislav Petkov <bp@alien8.de>, Minchan Kim <minchan@kernel.org>,
Mel Gorman <mgorman@techsingularity.net>,
Juri Lelli <juri.lelli@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
regressions@lists.linux.dev, riel@surriel.com,
viro@zeniv.linux.org.uk
Subject: Re: vchiq: Performance regression since 5.18-rc1
Date: Mon, 23 May 2022 08:19:41 +0200 [thread overview]
Message-ID: <e0503433-615d-3834-4392-d0868caf47cf@i2se.com> (raw)
In-Reply-To: <20220523044818.GS1790663@paulmck-ThinkPad-P17-Gen-1>
Hi Paul,
Am 23.05.22 um 06:48 schrieb Paul E. McKenney:
> On Sun, May 22, 2022 at 05:11:36PM +0200, Stefan Wahren wrote:
>> Hi Paul,
>>
>> Am 22.05.22 um 01:46 schrieb Paul E. McKenney:
>>> On Sun, May 22, 2022 at 01:22:00AM +0200, Stefan Wahren wrote:
>>>> Hi,
>>>>
>>>> while testing the staging/vc04_services/interface/vchiq_arm driver with my
>>>> Raspberry Pi 3 B+ (multi_v7_defconfig) i noticed a huge performance
>>>> regression since [ff042f4a9b050895a42cae893cc01fa2ca81b95c] mm:
>>>> lru_cache_disable: replace work queue synchronization with synchronize_rcu
>>>>
>>>> Usually i run "vchiq_test -f 1" to see the driver is still working [1].
>>>>
>>>> Before commit:
>>>>
>>>> real 0m1,500s
>>>> user 0m0,068s
>>>> sys 0m0,846s
>>>>
>>>> After commit:
>>>>
>>>> real 7m11,449s
>>>> user 0m2,049s
>>>> sys 0m0,023s
>>>>
>>>> Best regards
>>>>
>>>> [1] - https://github.com/raspberrypi/userland
>>> Please feel free to try the patch shown below. Or the pair of patches
>>> from Rik here:
>>>
>>> https://lore.kernel.org/lkml/20220218183114.2867528-2-riel@surriel.com/
>>> https://lore.kernel.org/lkml/20220218183114.2867528-3-riel@surriel.com/
>> I tried your patch and Rik's patches but in both cases vchiq_test runs 7
>> minutes instead of ~ 1 second.
> That is surprising. Do you boot with rcupdate.rcu_normal=1?
No, not explicit.
> That would
> nullify my patch, but I would expect that Rik's patch would still provide
> increased performance even in that case.
I will retest with a fresh SD card image.
>
> Could you please characterize where the slowdown is occurring?
Unfortunately i don't have a deep insight into driver and vchiq_test
tool. Just a user view.
Do you think an strace would be a good starting point?
@Phil Any advices to analyse this issue?
>
> Thanx, Paul
>
>> Best regards
>>
>>> There is work ongoing to produce something better, but ongoing slowly.
>>> Especially my part of that work.
>>>
>>> Thanx, Paul
>>>
>>> ------------------------------------------------------------------------
>>>
>>> From paulmck@kernel.org Mon Feb 14 11:05:49 2022
>>> Date: Mon, 14 Feb 2022 11:05:49 -0800
>>> From: "Paul E. McKenney" <paulmck@kernel.org>
>>> To: clm@fb.com
>>> Cc: riel@surriel.com, viro@zeniv.linux.org.uk, linux-kernel@vger.kernel.org,
>>> linux-fsdevel@vger.kernel.org, kernel-team@fb.com
>>> Subject: [PATCH RFC fs/namespace] Make kern_unmount() use
>>> synchronize_rcu_expedited()
>>> Message-ID: <20220214190549.GA2815154@paulmck-ThinkPad-P17-Gen-1>
>>> Reply-To: paulmck@kernel.org
>>> MIME-Version: 1.0
>>> Content-Type: text/plain; charset=us-ascii
>>> Content-Disposition: inline
>>> Status: RO
>>> Content-Length: 1036
>>> Lines: 32
>>>
>>> Experimental. Not for inclusion. Yet, anyway.
>>>
>>> Freeing large numbers of namespaces in quick succession can result in
>>> a bottleneck on the synchronize_rcu() invoked from kern_unmount().
>>> This patch applies the synchronize_rcu_expedited() hammer to allow
>>> further testing and fault isolation.
>>>
>>> Hey, at least there was no need to change the comment! ;-)
>>>
>>> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
>>> Cc: <linux-fsdevel@vger.kernel.org>
>>> Cc: <linux-kernel@vger.kernel.org>
>>> Not-yet-signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>>>
>>> ---
>>>
>>> namespace.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/fs/namespace.c b/fs/namespace.c
>>> index 40b994a29e90d..79c50ad0ade5b 100644
>>> --- a/fs/namespace.c
>>> +++ b/fs/namespace.c
>>> @@ -4389,7 +4389,7 @@ void kern_unmount(struct vfsmount *mnt)
>>> /* release long term mount so mount point can be released */
>>> if (!IS_ERR_OR_NULL(mnt)) {
>>> real_mount(mnt)->mnt_ns = NULL;
>>> - synchronize_rcu(); /* yecchhh... */
>>> + synchronize_rcu_expedited(); /* yecchhh... */
>>> mntput(mnt);
>>> }
>>> }
>>>
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next prev parent reply other threads:[~2022-05-23 9:20 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-21 23:22 vchiq: Performance regression since 5.18-rc1 Stefan Wahren
2022-05-21 23:46 ` Paul E. McKenney
2022-05-22 15:11 ` Stefan Wahren
2022-05-23 4:48 ` Paul E. McKenney
2022-05-23 6:19 ` Stefan Wahren [this message]
2022-05-23 9:29 ` Phil Elwell
2022-05-23 10:48 ` Stefan Wahren
2022-05-23 11:01 ` Phil Elwell
2022-05-23 11:15 ` Stefan Wahren
2022-05-23 11:22 ` Phil Elwell
2022-05-23 7:09 ` Sebastian Andrzej Siewior
2022-05-25 13:56 ` Marcelo Tosatti
2022-05-25 14:07 ` Stefan Wahren
2022-05-25 14:26 ` Sebastian Andrzej Siewior
2022-05-25 15:02 ` Paul E. McKenney
2022-05-25 15:37 ` Marcelo Tosatti
2022-05-29 22:47 ` Stefan Wahren
2022-05-30 9:54 ` Stefan Wahren
2022-05-23 9:28 ` Thorsten Leemhuis
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