From mboxrd@z Thu Jan 1 00:00:00 1970 From: FUJITA Tomonori Subject: Re: [PATCH 03/13] scsi: unify allocation of scsi command and sense buffer Date: Wed, 27 May 2009 10:36:40 +0900 Message-ID: <20090527103637W.fujita.tomonori@lab.ntt.co.jp> References: <1243349222.2815.22.camel@localhost.localdomain> <20090527003152X.fujita.tomonori@lab.ntt.co.jp> <4A1C1331.8060304@panasas.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: fujita.tomonori@lab.ntt.co.jp, James.Bottomley@HansenPartnership.com, jens.axboe@oracle.com, rdreier@cisco.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, chris.mason@oracle.com, david@fromorbit.com, hch@infradead.org, akpm@linux-foundation.org, jack@suse.cz, yanmin_zhang@linux.intel.com, linux-scsi@vger.kernel.org To: bharrosh@panasas.com Return-path: In-Reply-To: <4A1C1331.8060304@panasas.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Tue, 26 May 2009 19:05:05 +0300 Boaz Harrosh wrote: > On 05/26/2009 06:31 PM, FUJITA Tomonori wrote: > > > > Can we just fix some drivers not to do the DMA with the sense buffer in > > scsi_cmnd? IIRC, there are only five or six drivers that do such. > > This is not so. > All drivers that go through scsi_eh_prep_cmnd() will eventually DMA through > the regular read path. Including all the drivers that do nothing and let > scsi-ml do the REQUEST_SENSE > > Actually I have exact numbers, from the last time I did all that Hmm, we discussed this before, I think. scsi-ml uses scsi_eh_prep_cmnd only via scsi_send_eh_cmnd(). There are some users of scsi_send_eh_cmnd in scsi-ml but only scsi_request_sense does the DMA in the sense_buffer of scsi_cmnd. Only scsi_error_handler() uses scsi_request_sense() and scsi_send_eh_cmnd() works synchronously. So scsi-ml can easily avoid the the DMA in the sense_buffer of scsi_cmnd if we have one sense buffer per scsi_host.