From: Christoph Hellwig <hch@infradead.org>
To: Matthew Wilcox <willy@linux.intel.com>
Cc: linux-scsi@vger.kernel.org, DL-MPTFusionLinux@lsi.com
Subject: Re: [PATCH 2/2] mpt2sas: Reduce cache misses in command submission path
Date: Wed, 6 Apr 2011 09:46:55 -0400 [thread overview]
Message-ID: <20110406134654.GB21729@infradead.org> (raw)
In-Reply-To: <20110405214714.GR4183@linux.intel.com>
On Tue, Apr 05, 2011 at 05:47:14PM -0400, Matthew Wilcox wrote:
>
> In a high-IOPS workload, mpt2sas_base_get_smid_scsiio shows up in the top
> 20 cache misses. This is because the data structure used for allocating
> SMIDs is cache unfriendly; freed SMIDs are placed on the tail of the list,
> guaranteeing a cache miss by the time we allocate it again.
>
> By placing the freed SMID at the head of the list, we increase the
> likelihood of it being cache-hot when it's used again.
Looks good for now. But given that the smids are a statically allocated
ressource it might be a good idea to get rid of all the rather cache
unfriendly linked lists and locking and use a bitmap to allocate
smids and then just index into a linear array of them.
next prev parent reply other threads:[~2011-04-06 13:46 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-05 21:47 [PATCH 2/2] mpt2sas: Reduce cache misses in command submission path Matthew Wilcox
2011-04-06 13:46 ` Christoph Hellwig [this message]
2011-04-07 5:26 ` Matthew Wilcox
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