Re: [PATCH 3/3] brlocks/lglocks: turn into functions

From: Nick Piggin
Date: Wed May 09 2012 - 03:35:59 EST

On 7 May 2012 13:39, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:
> On Fri, 20 Apr 2012 21:21:49 +1000, Nick Piggin <npiggin@xxxxxxxxx> wrote:
>> This still not merged?
> No, I've been away. ÂI've put it in -next for tomorrow, though I'm not
> sure what the best way to get it to Linus next merge window.
>> There is a reason, which is performance. Extra function call, but also
>> IIRC the percpu accessor was not so fast doing it this way. Maybe
>> that's improved...
>> So what's the performance difference?
> What benchmarks you usually run? ÂFeel free to try it out and report
> back; I only have small hardware here.

Nothing big. The actual scalability should be unchanged, because you're
not going to be dirtying any shared cachelines. It's the use of dynamic
percpu allocator and out of line calls etc which will slow down straight
line performance.

How many microseconds does it take to stat("./dir1/dir2/myfile"), for

`git diff` of a large tree, for something more realistic but still going to
exercise that path.
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