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/ 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); } }
