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Message-ID: <20160608085837.GA10792@gmail.com>
Date: Wed, 8 Jun 2016 10:58:37 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Waiman Long <waiman.long@....com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Dave Hansen <dave.hansen@...el.com>,
"Chen, Tim C" <tim.c.chen@...el.com>,
Ingo Molnar <mingo@...hat.com>,
Davidlohr Bueso <dbueso@...e.de>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Jason Low <jason.low2@...com>,
Michel Lespinasse <walken@...gle.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Waiman Long <waiman.long@...com>,
Al Viro <viro@...iv.linux.org.uk>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: performance delta after VFS i_mutex=>i_rwsem conversion
* Waiman Long <waiman.long@....com> wrote:
> I do have a patchset that allow us to more accurately determine the state of
> the lock owner.
>
> locking/rwsem: Add reader-owned state to the owner field
> http://www.spinics.net/lists/kernel/msg2258572.html
>
> That should eliminate the performance gap between mutex and rwsem wrt
> spinning when only writers are present. I am hoping that that patchset can
> be queued for 4.8.
Yeah, so I actually had this series merged for testing last week, but a
complication with a prereq patch made me unmerge it. But I have no fundamental
objections, at all.
I also agree with Linus's general observation that we want to make
down_write()/up_write() match mutex performance characteristics.
I think kernel developers should fundamentally be able to switch between
mutex_lock()/unlock() and down_write()/up_write() and back, without noticing
any high level behavioral changes.
Any 'reader/writer mixing' artifacts are secondary concerns and we'll sort them
out as they happen.
Thanks,
Ingo
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