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From: Tejun Heo <htejun@gmail.com>
To: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>,
	Mark Mason <mason@postdiluvian.org>,
	linux-ide@vger.kernel.org, jgarzik@pobox.com,
	Jens Axboe <jens.axboe@oracle.com>
Subject: Re: [PATCH] scsi: align shost->hostdata to cacheline
Date: Fri, 15 Feb 2008 07:49:03 +0900	[thread overview]
Message-ID: <47B4C55F.1070806@gmail.com> (raw)
In-Reply-To: <1203001520.3189.11.camel@localhost.localdomain>

James Bottomley wrote:
> On Thu, 2008-02-14 at 18:48 +0900, Tejun Heo wrote:
>> shost->hostdata can contain arbitrary data including DMA target
>> buffers.  Align it to cacheline.
>>
>> Signed-off-by: Tejun Heo <htejun@gmail.com>
>> ---
>> James, what do you think?
> 
> Hmm, it will blow out the host size ... although that's not such a huge
> problem since there are relatively few of them in most running kernels.
> What's the actual use case for this, though?  The host structure is
> allocated in ordinary memory ... we don't make sure it's DMAable, and
> most HBAs that want to use memory for mailboxes need coherent memory
> anyway.

"As it can contain arbitrary structure, it should follow the largest
meaningful alignment to allow the contained structure proper alignment."
is the logic.  I think it's generally RTTD for inline private data but
feel free to disagree.

Thanks.

-- 
tejun

  reply	other threads:[~2008-02-14 22:49 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-12 18:02 libata/sata_sil24 cache alignment problem? Mark Mason
2008-02-12 22:12 ` Alan Cox
2008-02-12 23:36   ` James Bottomley
2008-02-13  2:13     ` Alan Cox
2008-02-13  2:32       ` James Bottomley
2008-02-13 18:47   ` Mark Mason
2008-02-13 20:21     ` Alan Cox
2008-02-13 21:25       ` Mark Mason
2008-02-14  0:21         ` Alan Cox
2008-02-14  3:05           ` Tejun Heo
2008-02-14  9:44             ` [PATCH] libata: align ap->sector_buf to cacheline Tejun Heo
2008-02-14  9:48             ` [PATCH] scsi: align shost->hostdata " Tejun Heo
2008-02-14 15:05               ` James Bottomley
2008-02-14 22:49                 ` Tejun Heo [this message]
2008-02-15 18:57                   ` James Bottomley
2008-02-21  2:32                     ` Tejun Heo
2008-02-13 18:51   ` libata/sata_sil24 cache alignment problem? Mark Mason
2008-02-12 23:25 ` Thomas Evans

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