Re: [PATCH v4 0/5] kernfs: proposed locking and concurrency improvement

[Fox Chen]

Hi Ian

On Thu, May 13, 2021 at 10:10 PM Ian Kent <raven@xxxxxxxxxx> wrote:
>
> On Wed, 2021-05-12 at 16:54 +0800, Fox Chen wrote:
> > On Wed, May 12, 2021 at 4:47 PM Fox Chen <foxhlchen@xxxxxxxxx> wrote:
> > >
> > > Hi,
> > >
> > > I ran it on my benchmark (
> > > https://github.com/foxhlchen/sysfs_benchmark).
> > >
> > > machine: aws c5 (Intel Xeon with 96 logical cores)
> > > kernel: v5.12
> > > benchmark: create 96 threads and bind them to each core then run
> > > open+read+close on a sysfs file simultaneously for 1000 times.
> > > result:
> > > Without the patchset, an open+read+close operation takes 550-570
> > > us,
> > > perf shows significant time(>40%) spending on mutex_lock.
> > > After applying it, it takes 410-440 us for that operation and perf
> > > shows only ~4% time on mutex_lock.
> > >
> > > It's weird, I don't see a huge performance boost compared to v2,
> > > even
> >
> > I meant I don't see a huge performance boost here and it's way worse
> > than v2.
> > IIRC, for v2 fastest one only takes 40us
>
> Thanks Fox,
>
> I'll have a look at those reports but this is puzzling.
>
> Perhaps the added overhead of the check if an update is
> needed is taking more than expected and more than just
> taking the lock and being done with it. Then there's
> the v2 series ... I'll see if I can dig out your reports
> on those too.

Apologies, I was mistaken, it's compared to V3, not V2.  The previous
benchmark report is here.
https://lore.kernel.org/linux-fsdevel/CAC2o3DKNc=sL2n8291Dpiyb0bRHaX=nd33ogvO_LkJqpBj-YmA@xxxxxxxxxxxxxx/

> >
> >
> > > though there is no mutex problem from the perf report.
> > > I've put console outputs and perf reports on the attachment for
> > > your reference.
>
> Yep, thanks.
> Ian
>

thanks,
fox