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Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands |
Date: |
Mon, 4 Mar 2013 13:58:06 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Thu, Feb 28, 2013 at 03:24:27PM +0000, Dietmar Maurer wrote:
> > > Unfortunately, NBD add considerable overheads. I guess the socket
> > communications copies data.
> > > This is really unnecessary if I can write directly to the output stream.
> >
> > The disk is the bottleneck, not memory bandwidth. Hard disks only do
> > 10-100 MB/sec and SSDs only do a couple 100 MB/sec. Memory copy is
> > insignificant compared to the I/O activity required to copy out the entire
> > disk
> > image, not to mention delaying guest writes until we read the original data
> > from
> > the disk.
> >
> > Unless there's a concrete performance problem here this is premature
> > optimization.
>
> I currently test with about 700MB read speed, and get a slow down by factor
> 1.7.
> So memory copy is very significant , or there is something wrong with nbd.c.
What are the details of the test?
Is it using 64 KB writes and have you tried 256 KB writes?
Stefan
- Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands,
Stefan Hajnoczi <=
- Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands, Dietmar Maurer, 2013/03/04
- Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands, Kevin Wolf, 2013/03/04
- Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands, Dietmar Maurer, 2013/03/04
- Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands, Stefan Hajnoczi, 2013/03/06
- Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands, Dietmar Maurer, 2013/03/06
- Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands, Kevin Wolf, 2013/03/06
- Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands, Dietmar Maurer, 2013/03/06
- Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands, Kevin Wolf, 2013/03/06
- Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands, Dietmar Maurer, 2013/03/06
- Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands, Kevin Wolf, 2013/03/07