Messages in this thread | | | Date | Thu, 9 Mar 2023 21:11:47 -0800 | From | Eric Biggers <> | Subject | Re: [PATCH] fsverity: Remove WQ_UNBOUND from fsverity read workqueue |
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On Thu, Mar 09, 2023 at 01:37:41PM -0800, Nathan Huckleberry wrote: > WQ_UNBOUND causes significant scheduler latency on ARM64/Android. This > is problematic for latency sensitive workloads like I/O post-processing. > > Removing WQ_UNBOUND gives a 96% reduction in fsverity workqueue related > scheduler latency and improves app cold startup times by ~30ms.
Maybe mention that WQ_UNBOUND was recently removed from the dm-verity workqueue too, for the same reason?
I'm still amazed that it's such a big improvement! I don't really need it to apply this patch, but it would be very interesting to know exactly why the latency is so bad with WQ_UNBOUND.
> > This code was tested by running Android app startup benchmarks and > measuring how long the fsverity workqueue spent in the ready queue. > > Before > Total workqueue scheduler latency: 553800us > After > Total workqueue scheduler latency: 18962us > > Change-Id: I693efee541757851ed6d229430111cd763d39067
No Change-Id in upstream patches, please.
> diff --git a/fs/verity/verify.c b/fs/verity/verify.c > index f50e3b5b52c9..e8ec37774d63 100644 > --- a/fs/verity/verify.c > +++ b/fs/verity/verify.c > @@ -395,7 +395,7 @@ int __init fsverity_init_workqueue(void) > * which blocks reads from completing, over regular application tasks. > */ > fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue", > - WQ_UNBOUND | WQ_HIGHPRI, > + WQ_HIGHPRI, > num_online_cpus());
There's a comment just above here that explains why WQ_UNBOUND is being used. It needs to be updated to explain why WQ_UNBOUND is *not* being used.
- Eric
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