Re: [GIT PULL] adaptive spinning mutexes

Bill Davidsen
2009-01-16T18:37:10Z

Chris Mason wrote:
> On Thu, 2009-01-15 at 10:16 -0800, Linus Torvalds wrote:
>> On Thu, 15 Jan 2009, Ingo Molnar wrote:
>>> btw., i think spin-mutexes have a design advantage here: in a lot of code
>>> areas it's quite difficult to use spinlocks - cannot allocate memory,
>>> cannot call any code that can sporadically block (but does not _normally_
>>> block), etc.
>>>
>>> With mutexes those atomicity constraints go away - and the performance
>>> profile should now be quite close to that of spinlocks as well.
>> Umm. Except if you wrote the code nicely and used spinlocks, you wouldn't
>> hold the lock over all those unnecessary and complex operations.
>>
>
> While this is true, there are examples of places we should expect
> speedups for this today.
>
> Concurrent file creation/deletion in a single dir will often find things
> hot in cache and not have to block anywhere (mail spools).
>
And although not as common, NNTP servers using file per article storage.

> Concurrent O_DIRECT aio writes to the same file, where i_mutex is
> dropped early on.
>
> pipes should see a huge improvement.
>
I'd like to see that. Didn't realize how slow pipes really are.

> I'll kick off some runs of my three benchmarks on ext3 for comparison.
> If there are things less synthetic people would like to see, please let
> me know.
>
> -chris
>
>
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--
Bill Davidsen <davidsen@tmr.com>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot