Messages in this thread | | | Date | Sun, 22 May 2022 17:11:36 +0200 | Subject | Re: vchiq: Performance regression since 5.18-rc1 | From | Stefan Wahren <> |
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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.
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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