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Message-ID: <CAMi7pMau=bOZ4ECPgteHT-NkfxU+oU0qZw+fFsjKfGQP_UscBw@mail.gmail.com> Date: Tue, 27 Nov 2012 14:25:27 -0800 From: Laine Walker-Avina <lwalkera@...e.org> To: Matthew Wilcox <willy@...ux.intel.com> Cc: Jens Axboe <axboe@...nel.dk>, linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org, lwalkera@...ron.com Subject: Re: Alignment Issue with Direct IO to NVMe Drive On Tue, Nov 27, 2012 at 1:39 PM, Matthew Wilcox <willy@...ux.intel.com> wrote: > 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@...ux.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. There is no mention of IOMMU in dmesg on a fresh boot. The processor in the test system I'm using is an i5-2400 (Sandy Bridge). -Laine -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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