On Thu, 2017-06-01 at 07:49 -0400, Benjamin Coddington wrote:
> On 1 Jun 2017, at 7:41, Jeff Layton wrote:
>
> > On Thu, 2017-06-01 at 10:05 +0800, kernel test robot wrote:
> > > Greeting,
> > >
> > > FYI, we noticed a -14.1% regression of will-it-scale.per_process_ops
> > > due to commit:
> > >
> > >
> > > commit: 9d21d181d06acab9a8e80eac2ec4eed77b656793 ("fs/locks: Set
> > > fl_nspid at file_lock allocation")
> > > url:
> > > https://github.com/0day-ci/linux/commits/Benjamin-Coddington/fs-locks-Alloc-file_lock-where-practical/20170527-050700
> > >
> > >
> >
> > Ouch, that's a rather nasty performance hit. In hindsight, maybe we
> > shouldn't move those off the stack after all? Heck, if it's that
> > significant, maybe we should move the F_SETLK callers to allocate
> > these
> > on the stack as well?
>
> We can do that. But, I think this is picking up the
> locks_mandatory_area()
> allocation which is now removed. The attached config has
> CONFIG_MANDATORY_FILE_LOCKING=y, so there's allocation on every
> read/write.
>
I'm not so sure. That would only be the case if the thing were marked
for manadatory locking (a really rare thing).
The test is really simple and I don't think any read/write activity is
involved:
https://github.com/antonblanchard/will-it-scale/blob/master/tests/lock1.c
...and the 0 day bisected it down to this patch, IIUC:
https://github.com/0day-ci/linux/commit/9d21d181d06acab9a8e80eac2ec4eed77b656793
It seems likely that it's the extra get_pid/put_pid in the allocation
and free codepath. I expected those to be pretty cheap, but maybe
they're not?
--
Jeff Layton <jlayton@xxxxxxxxxx>
--
To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
