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

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Date:	Mon, 22 Jun 2015 20:11:14 +0200
From:	Daniel Wagner <daniel.wagner@...-carit.de>
To:	Peter Zijlstra <peterz@...radead.org>, <oleg@...hat.com>,
	<paulmck@...ux.vnet.ibm.com>
CC:	<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 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...

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

flock01
                             mean   variance      sigma        max        min
                    4.1.0    11.7075   816.3341    28.5716   125.6552     0.0021
             percpu-rwsem    11.4614   760.1345    27.5705   132.5030     0.0026


flock02
                             mean   variance      sigma        max        min
                    4.1.0     7.0197     1.1812     1.0868    10.6188     5.1706
             percpu-rwsem     9.3194     1.3443     1.1594    11.5902     6.6138


lease01
                             mean   variance      sigma        max        min
                    4.1.0    41.8361    23.8462     4.8833    51.3493    28.5859
             percpu-rwsem    40.2738    20.8323     4.5642    49.6037    28.0704


lease02
                             mean   variance      sigma        max        min
                    4.1.0    71.2159    12.7763     3.5744    77.8432    58.0390
             percpu-rwsem    71.4312    14.7688     3.8430    76.5036    57.8615


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


posix03
                             mean   variance      sigma        max        min
                    4.1.0     0.9121     0.0000     0.0000     0.9121     0.9121
             percpu-rwsem     0.9379     0.0000     0.0000     0.9379     0.9379


posix04
                             mean   variance      sigma        max        min
                    4.1.0     0.0703     0.0044     0.0664     0.6764     0.0437
             percpu-rwsem     0.0675     0.0007     0.0267     0.3236     0.0491


cheers,
daniel

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