From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Nicholas A. Bellinger" Subject: Re: [PATCH RESEND 0/1] AHCI: Optimize interrupt processing Date: Fri, 19 Jul 2013 14:01:24 -0700 Message-ID: <1374267684.7397.1058.camel@haakon3.risingtidesystems.com> References: <20130711102630.GA11133@dhcp-26-207.brq.redhat.com> <1373583637.7397.370.camel@haakon3.risingtidesystems.com> <20130712074559.GA8727@dhcp-26-207.brq.redhat.com> <1373692812.7397.625.camel@haakon3.risingtidesystems.com> <20130716183207.GA6402@dhcp-26-207.brq.redhat.com> <1374010683.7397.880.camel@haakon3.risingtidesystems.com> <20130717161909.GB21468@dhcp-26-207.brq.redhat.com> <1374173515.7397.948.camel@haakon3.risingtidesystems.com> <51E83E32.9050306@cs.wisc.edu> <1374193399.7397.973.camel@haakon3.risingtidesystems.com> <20130719003034.GG28005@kernel.dk> <1374195825.7397.997.camel@haakon3.risingtidesystems.com> <1374215660.7397.1041.camel@haakon3.risingtidesystems.com> <1374248000.2266.20.camel@dabdike> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1374248000.2266.20.camel@dabdike> Sender: linux-kernel-owner@vger.kernel.org To: James Bottomley Cc: Jens Axboe , Mike Christie , Alexander Gordeev , Tejun Heo , linux-kernel@vger.kernel.org, linux-ide@vger.kernel.org, Jeff Garzik , linux-scsi List-Id: linux-ide@vger.kernel.org On Fri, 2013-07-19 at 08:33 -0700, James Bottomley wrote: > On Thu, 2013-07-18 at 23:34 -0700, Nicholas A. Bellinger wrote: > > diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c > > index 0101af5..191bc15 100644 > > --- a/drivers/ata/libata-scsi.c > > +++ b/drivers/ata/libata-scsi.c > > @@ -1144,7 +1144,11 @@ static int ata_scsi_dev_config(struct scsi_device *sdev, > > "sector_size=%u > PAGE_SIZE, PIO may malfunction\n", > > sdev->sector_size); > > > > - blk_queue_update_dma_alignment(q, sdev->sector_size - 1); > > + if (!q->mq_ops) { > > + blk_queue_update_dma_alignment(q, sdev->sector_size - 1); > > + } else { > > + printk("Skipping dma_alignment for libata w/ scsi-mq\n"); > > + } > > Amazingly enough there is a reason for the dma alignment, and it wasn't > just to annoy you, so you can't blindly do this. > > The email thread is probably lost in the mists of time, but if I > remember correctly the problem is that some ahci DMA controllers barf if > the sector they're doing DMA on crosses a page boundary. Some are > annoying enough to actually cause silent data corruption. You won't > find every ahci DMA controller doing this, so the change will work for > some, but it will be hard to identify those it won't work for until > people start losing data. Thanks for the extra background. So at least from what I gather thus far this shouldn't be an issue for initial testing with scsi-mq <-> libata w/ ata_piix. > > The correct fix, obviously, is to do the bio copy on the kernel path for > unaligned data. It is OK to assume that REQ_TYPE_FS data is correctly > aligned (because of the block to page alignment). > Indeed. Looking into the bio_copy_kern() breakage next.. --nab