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From: "J. Bruce Fields" <bfields@fieldses.org>
To: NeilBrown <neilb@suse.com>
Cc: Jeff Layton <jlayton@kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Martin Wilck <mwilck@suse.de>,
	linux-fsdevel@vger.kernel.org,
	Frank Filz <ffilzlnx@mindspring.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/5 - V2] locks: avoid thundering-herd wake-ups
Date: Fri, 10 Aug 2018 11:47:42 -0400
Message-ID: <20180810154742.GE7906@fieldses.org> (raw)
In-Reply-To: <87y3derjut.fsf@notabene.neil.brown.name>

On Fri, Aug 10, 2018 at 01:17:14PM +1000, NeilBrown wrote:
> On Thu, Aug 09 2018, J. Bruce Fields wrote:
> 
> > On Fri, Aug 10, 2018 at 11:50:58AM +1000, NeilBrown wrote:
> >> You're good at this game!
> >
> > Everybody's got to have a hobby, mine is pathological posix locking
> > cases....
> >
> >> So, because a locker with the same "owner" gets a free pass, you can
> >> *never* say that any lock which conflicts with A also conflicts with B,
> >> as a lock with the same owner as B will never conflict with B, even
> >> though it conflicts with A.
> >> 
> >> I think there is still value in having the tree, but when a waiter is
> >> attached under a new blocker, we need to walk the whole tree beneath the
> >> waiter and detach/wake anything that is not blocked by the new blocker.
> >
> > If you're walking the whole tree every time then it might as well be a
> > flat list, I think?
> 
> The advantage of a tree is that it keeps over-lapping locks closer
> together.
> For it to make a difference you would need a load where lots of threads
> were locking several different small ranges, and other threads were
> locking large ranges that cover all the small ranges.

OK, I'm not sure I understand, but I'll give another look at the next
version....

> I doubt this is common, but it doesn't seem as strange as other things
> I've seen in the wild.
> The other advantage, of course, is that I've already written the code,
> and I like it.
> 
> Maybe I'll do a simple-list version, then a patch to convert that to the
> clever-tree version, and we can then have something concrete to assess.

That might help, thanks.

--b.

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-09  2:04 NeilBrown
2018-08-09  2:04 ` [PATCH 1/5] fs/locks: rename some lists and pointers NeilBrown
2018-08-09  2:04 ` [PATCH 2/5] fs/locks: allow a lock request to block other requests NeilBrown
2018-08-09  2:04 ` [PATCH 3/5] fs/locks: change all *_conflict() functions to return a new enum NeilBrown
2018-08-09 11:09   ` Jeff Layton
2018-08-09 13:09   ` J. Bruce Fields
2018-08-09 23:40     ` NeilBrown
2018-08-10  0:56       ` J. Bruce Fields
2018-08-09  2:04 ` [PATCH 4/5] fs/locks: split out __locks_wake_one() NeilBrown
2018-08-09  2:04 ` [PATCH 5/5] fs/locks: create a tree of dependent requests NeilBrown
2018-08-09 11:17   ` Jeff Layton
2018-08-09 23:25     ` NeilBrown
2018-08-09 14:13   ` J. Bruce Fields
2018-08-09 22:19     ` NeilBrown
2018-08-10  0:36       ` J. Bruce Fields
2018-08-09 17:32 ` [PATCH 0/5 - V2] locks: avoid thundering-herd wake-ups J. Bruce Fields
2018-08-09 22:12   ` NeilBrown
2018-08-10  0:29     ` J. Bruce Fields
2018-08-10  1:50       ` NeilBrown
2018-08-10  2:52         ` J. Bruce Fields
2018-08-10  3:17           ` NeilBrown
2018-08-10 15:47             ` J. Bruce Fields [this message]
2018-08-11 11:56               ` Jeff Layton
2018-08-11 12:35                 ` J. Bruce Fields
2018-08-11 11:51       ` Jeff Layton
2018-08-11 12:21         ` J. Bruce Fields
2018-08-11 13:15           ` Jeff Layton

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