Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 23 May 2022 08:19:41 +0200 | Subject | Re: vchiq: Performance regression since 5.18-rc1 | From | Stefan Wahren <> |
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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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