From: Brian Foster <bfoster@redhat.com>
To: Dave Chinner <david@fromorbit.com>
Cc: xfs@oss.sgi.com
Subject: Re: [PATCH 4/5] libxfs: buffer cache hashing is suboptimal
Date: Fri, 13 Dec 2013 09:23:31 -0500 [thread overview]
Message-ID: <52AB1863.9070404@redhat.com> (raw)
In-Reply-To: <20131212205657.GA10988@dastard>
On 12/12/2013 03:56 PM, Dave Chinner wrote:
> On Thu, Dec 12, 2013 at 01:59:26PM -0500, Brian Foster wrote:
>> On 12/12/2013 02:22 AM, Dave Chinner wrote:
>>> From: Dave Chinner <dchinner@redhat.com>
>>>
>>> The hashkey calculation is very simplistic,and throws away an amount
>>> of entropy that should be folded into the hash. The result is
>>> sub-optimal distribution across the hash tables. For example, with a
>>> default 512 entry table, phase 2 results in this:
>>>
>> ...
>>> Modify the hash to be something more workable - steal the linux
>>> kernel inode hash calculation and try that:
>>>
>> ...
>>>
>>> Kinda says it all, really...
>>>
>>> Signed-off-by: Dave Chinner <dchinner@redhat.com>
>>> ---
>>
>> Results look nice and the algorithm seems to match the kernel variant,
>> but what about the 32-bit alternate prime/cache line values? Safe to
>> leave out..?
>
> The buffer cache uses a 64 bit key, regardless of the platform.
> Therefore the 64 bit variant is always needed. The kernel inode hash
> uses a 32 bit key on 32 bit systems, which is why there are two
> variants for it.
>
Ah.. xfs_bufkey->blkno is an xfs_daddr_t, which is an __int64_t. Thanks.
Reviewed-by: Brian Foster <bfoster@redhat.com>
> Cheers,
>
> Dave.
>
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next prev parent reply other threads:[~2013-12-13 14:23 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-12 7:22 [PATCH 0/5] xfs_repair: scalability inmprovements Dave Chinner
2013-12-12 7:22 ` [PATCH 1/5] repair: translation lookups limit scalability Dave Chinner
2013-12-12 18:26 ` Christoph Hellwig
2013-12-12 18:58 ` Brian Foster
2013-12-12 7:22 ` [PATCH 2/5] repair: per AG locks contend for cachelines Dave Chinner
2013-12-12 18:27 ` Christoph Hellwig
2013-12-12 18:58 ` Brian Foster
2013-12-12 20:46 ` Dave Chinner
2013-12-12 7:22 ` [PATCH 3/5] repair: phase 6 is trivially parallelisable Dave Chinner
2013-12-12 18:43 ` Christoph Hellwig
2013-12-12 20:53 ` Dave Chinner
2013-12-12 18:59 ` Brian Foster
2013-12-12 7:22 ` [PATCH 4/5] libxfs: buffer cache hashing is suboptimal Dave Chinner
2013-12-12 18:28 ` Christoph Hellwig
2013-12-12 18:59 ` Brian Foster
2013-12-12 20:56 ` Dave Chinner
2013-12-13 14:23 ` Brian Foster [this message]
2013-12-12 7:22 ` [PATCH 5/5] repair: limit auto-striding concurrency apprpriately Dave Chinner
2013-12-12 18:29 ` Christoph Hellwig
2013-12-12 21:00 ` Dave Chinner
2013-12-12 18:59 ` Brian Foster
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