From: willy@linux.intel.com (Matthew Wilcox)
Subject: Alignment Issue with Direct IO to NVMe Drive
Date: Tue, 27 Nov 2012 16:39:43 -0500 [thread overview]
Message-ID: <20121127213943.GB5100@linux.intel.com> (raw)
In-Reply-To: <CAMi7pMb7Ln02hLfa_i-7ucWZBDGzQLUOoQTeFp70=yGix_gojA@mail.gmail.com>
On Tue, Nov 27, 2012@09:47:48AM -0800, Laine Walker-Avina wrote:
> On Tue, Nov 27, 2012@9:05 AM, Matthew Wilcox <willy@linux.intel.com> wrote:
> > Laine, when this occurs, what is the alignment of 'offset' in the sg
> > entry you're looking at? If userspace is passing in an unaligned address,
> > I don't think there's anything we do to try to align it.
>
> I thought this was the case as well, but it appears to be aligned
> looking at the request in the user space program (fio using libaio in
> this case) before the IO is submitted.
OK, so we have an aligned virtual address being translated into an
unaligned DMA address. I have a suspicion ... are you using the swiotlb,
or are you using a real IOMMU? Grep dmesg for 'IOMMU' if you're not sure.
WARNING: multiple messages have this Message-ID (diff)
From: Matthew Wilcox <willy@linux.intel.com>
To: Laine Walker-Avina <lwalkera@ieee.org>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org,
lwalkera@micron.com
Subject: Re: Alignment Issue with Direct IO to NVMe Drive
Date: Tue, 27 Nov 2012 16:39:43 -0500 [thread overview]
Message-ID: <20121127213943.GB5100@linux.intel.com> (raw)
In-Reply-To: <CAMi7pMb7Ln02hLfa_i-7ucWZBDGzQLUOoQTeFp70=yGix_gojA@mail.gmail.com>
On Tue, Nov 27, 2012 at 09:47:48AM -0800, Laine Walker-Avina wrote:
> On Tue, Nov 27, 2012 at 9:05 AM, Matthew Wilcox <willy@linux.intel.com> wrote:
> > Laine, when this occurs, what is the alignment of 'offset' in the sg
> > entry you're looking at? If userspace is passing in an unaligned address,
> > I don't think there's anything we do to try to align it.
>
> I thought this was the case as well, but it appears to be aligned
> looking at the request in the user space program (fio using libaio in
> this case) before the IO is submitted.
OK, so we have an aligned virtual address being translated into an
unaligned DMA address. I have a suspicion ... are you using the swiotlb,
or are you using a real IOMMU? Grep dmesg for 'IOMMU' if you're not sure.
next prev parent reply other threads:[~2012-11-27 21:39 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-27 0:35 Alignment Issue with Direct IO to NVMe Drive Laine Walker-Avina
2012-11-27 0:35 ` Laine Walker-Avina
2012-11-27 12:09 ` Jens Axboe
2012-11-27 12:09 ` Jens Axboe
2012-11-27 17:05 ` Matthew Wilcox
2012-11-27 17:05 ` Matthew Wilcox
2012-11-27 17:47 ` Laine Walker-Avina
2012-11-27 17:47 ` Laine Walker-Avina
2012-11-27 21:39 ` Matthew Wilcox [this message]
2012-11-27 21:39 ` Matthew Wilcox
2012-11-27 22:25 ` Laine Walker-Avina
2012-11-27 22:25 ` Laine Walker-Avina
2012-11-27 17:43 ` Laine Walker-Avina
2012-11-27 17:43 ` Laine Walker-Avina
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