linux-kernel - Re: [PATCH RFC 0/4] change sb_writers to use percpu_rw

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Message-ID: <20150716085551.GH22847@quack.suse.cz>
Date:	Thu, 16 Jul 2015 10:55:51 +0200
From:	Jan Kara <jack@...e.cz>
To:	Dave Hansen <dave.hansen@...ux.intel.com>
Cc:	Jan Kara <jack@...e.cz>, Oleg Nesterov <oleg@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Daniel Wagner <daniel.wagner@...-carit.de>,
	Davidlohr Bueso <dave@...olabs.net>,
	Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 0/4] change sb_writers to use percpu_rw_semaphore

On Thu 16-07-15 00:30:27, Dave Hansen wrote:
> On 07/16/2015 12:26 AM, Jan Kara wrote:
> > So Dave's patches would go in only in the next merge window anyway so we
> > still have like two-three weeks to decide which patchset to take. If you
> > think it will take you longer, then merging Dave's patches makes some sense
> > although I personally don't think the issue is so important that we have to
> > fix it ASAP and eventual delay of one more release would be OK for me.
> 
> I thought of one more thing.
> 
> Oleg's patches are fast in the uncontended case.  My testing of his code
> so far was all single-threaded.  Will it slow down if we throw a bunch
> of threads at it an see contention?  I don't think my RCU approach will.
> 
> I can benchmark in the next few days on a larger machine.

Well, his semaphore is percpu as well so I don't think there should be a
difference (there may be some difference when freeze is in progress but
that doesn't really matter). But it's always good to verify.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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