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Date: Tue, 7 Jan 2014 20:37:23 +0200 From: Sergey Meirovich <rathamahata@...il.com> To: Christoph Hellwig <hch@...radead.org> Cc: Jan Kara <jack@...e.cz>, linux-scsi <linux-scsi@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Gluk <git.user@...il.com> Subject: Re: Terrible performance of sequential O_DIRECT 4k writes in SAN environment. ~3 times slower then Solars 10 with the same HBA/Storage. Hi Christoph, On 7 January 2014 17:58, Christoph Hellwig <hch@...radead.org> wrote: > On Mon, Jan 06, 2014 at 09:10:32PM +0100, Jan Kara wrote: >> This is likely a problem of Linux direct IO implementation. The thing is >> that in Linux when you are doing appending direct IO (i.e., direct IO which >> changes file size), the IO is performed synchronously so that we have our >> life simpler with inode size update etc. (and frankly our current locking >> rules make inode size update on IO completion almost impossible). Since >> appending direct IO isn't very common, we seem to get away with this >> simplification just fine... > > Shouldn't be too much of a problem at least for XFS and maybe even ext4 > with the workqueue based I/O end handler. For XFS we protect size > updates by the ilock which we already taken in that handler, not sure > what ext4 would do there. > Actually my initial report (14.67Mb/sec 3755.41 Requests/sec) was about ext4 However I have tried XFS as well. It was a bit slower than ext4 on all occasions. On the same machine results for XFS were: 13.97Mb/sec 3576..27 Requests/sec /dev/mapper/mpathc on /mnt/xfs type xfs (rw,noatime,nodiratime,nobarrier) -- 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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