From: Ming Lei <ming.lei@redhat.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Dave Chinner <dchinner@redhat.com>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>,
"Darrick J . Wong" <darrick.wong@oracle.com>,
xfs@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
Bart Van Assche <bvanassche@acm.org>,
Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH 1/5] block: warn on un-aligned DMA IO buffer
Date: Fri, 19 Oct 2018 09:39:12 +0800 [thread overview]
Message-ID: <20181019013912.GB13384@ming.t460p> (raw)
In-Reply-To: <2d9acd14-89ca-2304-75da-6e15240119f3@kernel.dk>
On Thu, Oct 18, 2018 at 07:33:50PM -0600, Jens Axboe wrote:
> On 10/18/18 7:28 PM, Ming Lei wrote:
> > On Thu, Oct 18, 2018 at 08:27:28AM -0600, Jens Axboe wrote:
> >> On 10/18/18 7:18 AM, Ming Lei wrote:
> >>> Now we only check if DMA IO buffer is aligned to queue_dma_alignment()
> >>> for pass-through request, and it isn't done for normal IO request.
> >>>
> >>> Given the check has to be done on each bvec, it isn't efficient to add the
> >>> check in generic_make_request_checks().
> >>>
> >>> This patch addes one WARN in blk_queue_split() for capturing this issue.
> >>
> >> I don't want to do this, because then we are forever doomed to
> >> have something that fully loops a bio at submission time. I
> >> absolutely hate the splitting we have and the need for it,
> >> hopefully it can go away for a subset of IOs at some point.
> >>
> >> In many ways, this seems to be somewhat of a made-up problem, I don't
> >> recall a single bug report for something like this over decades of
> >> working with the IO stack. 512b alignment restrictions for DMA seems
> >> absolutely insane. I know people claim they exist, but clearly that
> >> isn't a hard requirement or we would have been boned years ago.
> >
> > There are still some drivers with this requirement:
> >
> > drivers/ata/libata-scsi.c:1308: blk_queue_update_dma_alignment(q, sdev->sector_size - 1);
> > drivers/ata/pata_macio.c:812: blk_queue_update_dma_alignment(sdev->request_queue, 31);
> > drivers/ata/pata_macio.c:827: blk_queue_update_dma_alignment(sdev->request_queue, 15);
> > drivers/block/ps3disk.c:470: blk_queue_dma_alignment(queue, dev->blk_size-1);
> > drivers/block/rsxx/dev.c:282: blk_queue_dma_alignment(card->queue, blk_size - 1);
> > drivers/block/xen-blkfront.c:957: blk_queue_dma_alignment(rq, 511);
> > drivers/ide/ide-cd.c:1512: blk_queue_dma_alignment(q, 31);
> > drivers/message/fusion/mptscsih.c:2388: blk_queue_dma_alignment (sdev->request_queue, 512 - 1);
> > drivers/staging/rts5208/rtsx.c:94: blk_queue_dma_alignment(sdev->request_queue, (512 - 1));
> > drivers/usb/image/microtek.c:329: blk_queue_dma_alignment(s->request_queue, (512 - 1));
> > drivers/usb/storage/scsiglue.c:92: blk_queue_update_dma_alignment(sdev->request_queue, (512 - 1));
> > drivers/usb/storage/uas.c:818: blk_queue_update_dma_alignment(sdev->request_queue, (512 - 1));
>
> Of course, I too can grep :-)
>
> My point is that these settings might not match reality. And the
> WARN_ON(), as implemented, is going to trigger on any device that
> DOESN'T set the alignment, as Bart pointed out.
It is just a WARN_ON_ONCE() which exactly shows something which need
further attention, then related people may take a look and we can move
on.
So I think it is correct thing to do.
Thanks,
Ming
next prev parent reply other threads:[~2018-10-19 9:43 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-18 13:18 [PATCH 0/5] block: introduce helpers for allocating io buffer from slab Ming Lei
2018-10-18 13:18 ` [PATCH 1/5] block: warn on un-aligned DMA IO buffer Ming Lei
2018-10-18 14:27 ` Jens Axboe
2018-10-18 14:43 ` Christoph Hellwig
2018-10-18 14:46 ` Jens Axboe
2018-10-19 1:28 ` Ming Lei
2018-10-19 1:33 ` Jens Axboe
2018-10-19 1:39 ` Ming Lei [this message]
2018-10-19 1:52 ` Jens Axboe
2018-10-19 2:06 ` Ming Lei
2018-10-19 2:10 ` Jens Axboe
2018-10-18 14:28 ` Christoph Hellwig
2018-10-18 13:18 ` [PATCH 2/5] block: move .dma_alignment into q->limits Ming Lei
2018-10-18 14:29 ` Christoph Hellwig
2018-10-18 20:36 ` Bart Van Assche
2018-10-18 13:18 ` [PATCH 3/5] block: make dma_alignment as stacked limit Ming Lei
2018-10-18 14:31 ` Christoph Hellwig
2018-10-18 13:18 ` [PATCH 4/5] block: introduce helpers for allocating IO buffers from slab Ming Lei
2018-10-18 14:42 ` Christoph Hellwig
2018-10-18 15:11 ` Matthew Wilcox
2018-10-18 15:22 ` Christoph Hellwig
2018-10-19 2:53 ` Ming Lei
2018-10-19 4:06 ` Jens Axboe
2018-10-19 5:43 ` Dave Chinner
2018-10-18 13:18 ` [PATCH 5/5] xfs: use block layer helpers to allocate io buffer " Ming Lei
2018-10-18 14:03 ` [PATCH 0/5] block: introduce helpers for allocating " Matthew Wilcox
2018-10-18 14:05 ` Christoph Hellwig
2018-10-18 15:06 ` Matthew Wilcox
2018-10-18 15:21 ` Christoph Hellwig
2018-10-18 15:50 ` Bart Van Assche
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