From: Jeff Moyer <jmoyer@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Chris Mason <chris.mason@oracle.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: aio: bump i_count instead of using igrab
Date: Mon, 23 Aug 2010 17:18:41 -0400 [thread overview]
Message-ID: <x4962z12fke.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <20100823145031.GA1279@infradead.org> (Christoph Hellwig's message of "Mon, 23 Aug 2010 10:50:31 -0400")
Christoph Hellwig <hch@infradead.org> writes:
> On Mon, Aug 23, 2010 at 10:47:55AM -0400, Chris Mason wrote:
>> The aio batching code is using igrab to get an extra reference on the
>> inode so it can safely batch. igrab will go ahead and take the global
>> inode spinlock, which can be a bottleneck on large machines doing lots
>> of AIO.
>>
>> In this case, igrab isn't required because we already have a reference
>> on the file handle. It is safe to just bump the i_count directly
>> on the inode.
>>
>> Benchmarking shows this patch brings IOP/s on tons of flash up by about
>> 2.5X.
>
> There's some places in XFS where we do the same, and it showed up as a
> bottle neck before. Instead of open coding the increment we have
> a wrapper that includes and assert that the numbers is always positive.
>
> I think we really want a proper helper for general use instead of
> completly opencoding it.
Well, it would make detecting races or invalid assumptions a little
easier. If Chris wants to code that up, that's fine with me. Honestly,
though, I don't think it's necessary.
I've gone through the alloc/free paths for the inode and I'm convinced
this is safe. I'm happy with this version of the patch.
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
prev parent reply other threads:[~2010-08-23 21:18 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-23 14:47 aio: bump i_count instead of using igrab Chris Mason
2010-08-23 14:50 ` Christoph Hellwig
2010-08-23 15:00 ` Chris Mason
2010-08-23 17:26 ` Jeff Moyer
2010-08-24 7:33 ` Nick Piggin
2010-08-23 21:18 ` Jeff Moyer [this message]
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