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@xxxxxxxxxxx/ > > https://lore.kernel.org/lkml/20220218183114.2867528-3-riel@xxxxxxxxxxx/ > > 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? That would nullify my patch, but I would expect that Rik's patch would still provide increased performance even in that case. Could you please characterize where the slowdown is occurring? 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@xxxxxxxxxx Mon Feb 14 11:05:49 2022 > > Date: Mon, 14 Feb 2022 11:05:49 -0800 > > From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> > > To: clm@xxxxxx > > Cc: riel@xxxxxxxxxxx, viro@xxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, > > linux-fsdevel@xxxxxxxxxxxxxxx, kernel-team@xxxxxx > > Subject: [PATCH RFC fs/namespace] Make kern_unmount() use > > synchronize_rcu_expedited() > > Message-ID: <20220214190549.GA2815154@paulmck-ThinkPad-P17-Gen-1> > > Reply-To: paulmck@xxxxxxxxxx > > 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@xxxxxxxxxxxxxxxxxx> > > Cc: <linux-fsdevel@xxxxxxxxxxxxxxx> > > Cc: <linux-kernel@xxxxxxxxxxxxxxx> > > Not-yet-signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > > > --- > > > > 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); > > } > > } > >
