linux-kernel - Re: [RFC][PATCH 00/13] percpu rwsem -v2

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Date:	Mon, 22 Jun 2015 21:05:53 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Daniel Wagner <daniel.wagner@...-carit.de>
Cc:	oleg@...hat.com, paulmck@...ux.vnet.ibm.com, tj@...nel.org,
	mingo@...hat.com, linux-kernel@...r.kernel.org, der.herr@...r.at,
	dave@...olabs.net, riel@...hat.com, viro@...IV.linux.org.uk,
	torvalds@...ux-foundation.org
Subject: Re: [RFC][PATCH 00/13] percpu rwsem -v2

On Mon, Jun 22, 2015 at 08:11:14PM +0200, Daniel Wagner wrote:
> On 06/22/2015 02:16 PM, Peter Zijlstra wrote:
> > Also, since Linus thinks lglocks is a failed locking primitive (which I whole
> > heartedly agree with, its preempt-disable latencies are an abomination), it
> > also converts the global part of fs/locks's usage of lglock over to a
> > percpu-rwsem and uses a per-cpu spinlock for the local part. This both provides
> > another (4th) percpu-rwsem users and removes an lglock user.
> 
> I did a quick lockperf run with these patches on a 4 socket E5-4610 machine.
> These microbenches execercise the fs' locks a bit.
> 
> I suspect I got the wrong tree. The patches did not apply cleanly. The resulting
> kernel boots fine and doesn't explode... so far...

Its against tip/master, although I expect the locking/core bits that
were sent to Linus earlier today to be the biggest missing piece.

All I really did was build a kernel with lockdep enabled and boot +
build a kernel to see it didn't go belly up.

> The results aren't looking too bad. Though building a kernel with 'make -j200'
> was extreme slow. I'll look into it tomorrow.
> 
> https://git.samba.org/jlayton/linux.git/?p=jlayton/lockperf.git;a=summary

Sweet, I wasn't aware these existed. I'll go have a play.

> posix01
>                              mean   variance      sigma        max        min
>                     4.1.0   121.9020 27882.5260   166.9806   603.5509     0.0063
>              percpu-rwsem   185.3981 38474.3836   196.1489   580.6532     0.0073
> 
> 
> posix02
>                              mean   variance      sigma        max        min
>                     4.1.0    12.7461     3.1802     1.7833    15.5411     8.1018
>              percpu-rwsem    16.2341     4.3038     2.0746    19.3271    11.1751
> 

These two seem to hurt, lemme go look at what they do.
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