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Date: Wed, 6 Dec 2023 16:45:13 +0000
From: Al Viro <viro@zeniv.linux.org.uk>
To: Mateusz Guzik <mjguzik@gmail.com>
Cc: Oliver Sang <oliver.sang@intel.com>, oe-lkp@lists.linux.dev,
	lkp@intel.com, linux-fsdevel@vger.kernel.org,
	Christian Brauner <brauner@kernel.org>, linux-doc@vger.kernel.org,
	ying.huang@intel.com, feng.tang@intel.com, fengwei.yin@intel.com,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [viro-vfs:work.dcache2] [__dentry_kill()]  1b738f196e:
 stress-ng.sysinfo.ops_per_sec -27.2% regression
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On Wed, Dec 06, 2023 at 05:30:10PM +0100, Mateusz Guzik wrote:

> > What the hell is going on?  Was ->d_lock on parent serving as a throttle and reducing
> > the access rate to something badly contended down the road?  I don't see anything
> > of that sort in the profile changes, though...

> Not an outlandish claim would be that after you stopped taking one of
> them, spinning went down and more traffic was put on locks which *can*
> put their consumers off cpu (and which *do* do it in this test).

That's about the only guess I've got (see above), but if that's the case, which lock would
that be?

> All that said I think it would help if these reports started including
> off cpu time (along with bt) at least for spawned threads.