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Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support
From: |
Paul Brook |
Subject: |
Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support |
Date: |
Wed, 29 Apr 2009 12:37:20 +0100 |
User-agent: |
KMail/1.9.9 |
On Wednesday 29 April 2009, Christoph Hellwig wrote:
> On Wed, Apr 29, 2009 at 12:11:19PM +0100, Paul Brook wrote:
> > Is this actually measurably faster, or just infinitesimally faster in
> > theory?
>
> On normal disks it's rather theoretical. On high-end SSDs and arrays the
> impact is noticeable, mostly due to the additional latency.
How exactly does it introduce additional latency? A scsi command block is
hardly large or complicated. Are you suggesting that a 16/32byte scsi command
takes significantly longer to process than a 16byte virtio command
descriptor? I'd expect any extra processing to be a small fraction of the
host syscall latency, let alone the latency of the physical host adapter. It
probably even fits on the same CPU cache line.
Paul
- Re: [Qemu-devel] [PATCH] virtio-blk: add SGI_IO passthru support, (continued)
- [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Anthony Liguori, 2009/04/27
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Christoph Hellwig, 2009/04/28
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Anthony Liguori, 2009/04/28
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Christian Borntraeger, 2009/04/28
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Christoph Hellwig, 2009/04/29
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Paul Brook, 2009/04/29
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Christian Borntraeger, 2009/04/29
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Paul Brook, 2009/04/29
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Christoph Hellwig, 2009/04/29
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support,
Paul Brook <=
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Christoph Hellwig, 2009/04/30
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Paul Brook, 2009/04/30
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Javier Guerra, 2009/04/30
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Christian Borntraeger, 2009/04/28
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Christoph Hellwig, 2009/04/29
- Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support, Christian Borntraeger, 2009/04/29
[Qemu-devel] [PATCH 2/2] virtio-blk: add SG_IO passthru support, Christoph Hellwig, 2009/04/28