From: Christoph Hellwig <hch@lst.de>
To: Matthew Wilcox <willy@infradead.org>
Cc: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
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>
Subject: Re: [PATCH 0/5] block: introduce helpers for allocating io buffer from slab
Date: Thu, 18 Oct 2018 16:05:51 +0200 [thread overview]
Message-ID: <20181018140551.GA26500@lst.de> (raw)
In-Reply-To: <20181018140342.GB32429@bombadil.infradead.org>
On Thu, Oct 18, 2018 at 07:03:42AM -0700, Matthew Wilcox wrote:
> Before we go down this road, could we have a discussion about what
> hardware actually requires this? Storage has this weird assumption that
> I/Os must be at least 512 byte aligned in memory, and I don't know where
> this idea comes from. Network devices can do arbitrary byte alignment.
> Even USB controllers can do arbitrary byte alignment. Sure, performance
> is going to suck and there are definite risks on some architectures
> with doing IOs that are sub-cacheline aligned, but why is storage such a
> special snowflake that we assume that host controllers are only capable
> of doing 512-byte aligned DMAs?
Actually most storage controllers requires 4-byte alignment, but there is
a significant subset that requires 512-byte alignment.
next prev parent reply other threads:[~2018-10-18 22:07 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
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 [this message]
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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