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From: Tejun Heo <tj@kernel.org>
To: Jan Kara <jack@suse.cz>
Cc: Waiman Long <waiman.long@hpe.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Jan Kara <jack@suse.com>, Jeff Layton <jlayton@poochiereds.net>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	Christoph Lameter <cl@linux-foundation.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Andi Kleen <andi@firstfloor.org>,
	Dave Chinner <dchinner@redhat.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Scott J Norton <scott.norton@hpe.com>,
	Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [PATCH v2 1/7] lib/dlock-list: Distributed and lock-protected lists
Date: Thu, 14 Jul 2016 10:51:09 -0400	[thread overview]
Message-ID: <20160714145109.GI15005@htj.duckdns.org> (raw)
In-Reply-To: <20160714143547.GE13151@quack2.suse.cz>

Hello, Jan.

On Thu, Jul 14, 2016 at 04:35:47PM +0200, Jan Kara wrote:
> > > The current use case only need to use the regular lock functions. You are
> > > right that future use cases may require an irqsafe version of locks. I can
> > > either modify the code now to allow lock type selection at init time, for
> > > example, or defer it as a future enhancement when the need arises. What do
> > > you think?
> > 
> > The bulk of performance gain of dlist would come from being per-cpu
> > and I don't think it's likely that we'd see any noticeable difference
> > between irq and preempt safe operations.  Given that what's being
> > implemented is really low level operations, I'd suggest going with
> > irqsafe from the get-go.
> 
> I'm not sure here. i_sb_list for which percpu lists will be used is bashed
> pretty heavily under some workloads and the cost of additional interrupt
> disabling & enabling may be visible under those loads. Probably not in the
> cases where you get a boost from percpu lists but if the workload is mostly
> single-threaded, additional cpu cost may be measurable. So IMO we should
> check whether a load which creates tons of empty inodes in tmpfs from a
> single process doesn't regress with this change.

Sure, if it actually matters, we can always create separate preempt /
irq variants.

Thanks.

-- 
tejun

  reply	other threads:[~2016-07-14 14:51 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-07-11 17:32 [PATCH v2 0/7] vfs: Use dlock list for SB's s_inodes list Waiman Long
2016-07-11 17:32 ` [PATCH v2 1/7] lib/dlock-list: Distributed and lock-protected lists Waiman Long
2016-07-13 16:08   ` Tejun Heo
2016-07-14  2:54     ` Waiman Long
2016-07-14 11:50       ` Tejun Heo
2016-07-14 14:35         ` Jan Kara
2016-07-14 14:51           ` Tejun Heo [this message]
2016-07-14 16:16             ` Waiman Long
2016-07-14 17:13         ` Waiman Long
2016-07-14 17:41           ` Tejun Heo
2016-07-11 17:32 ` [PATCH v2 2/7] lib/dlock-list: Add __percpu modifier for parameters Waiman Long
2016-07-13 16:08   ` Tejun Heo
2016-07-14  2:54     ` Waiman Long
2016-07-11 17:32 ` [PATCH v2 3/7] fsnotify: Simplify inode iteration on umount Waiman Long
2016-07-11 17:32 ` [PATCH v2 4/7] vfs: Remove unnecessary list_for_each_entry_safe() variants Waiman Long
2016-07-11 17:32 ` [PATCH v2 5/7] vfs: Use dlock list for superblock's inode list Waiman Long
2016-07-11 17:32 ` [RFC PATCH v2 6/7] lib/persubnode: Introducing a simple per-subnode APIs Waiman Long
2016-07-12  3:14   ` Boqun Feng
2016-07-12 18:37     ` Waiman Long
2016-07-12 14:27   ` Tejun Heo
2016-07-12 18:51     ` Waiman Long
2016-07-12 18:57       ` Tejun Heo
2016-07-12 19:42         ` Waiman Long
2016-07-11 17:32 ` [RFC PATCH v2 7/7] lib/dlock-list: Use the per-subnode APIs for managing lists Waiman Long

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