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Re: [Qemu-devel] Effect of qemu-img convert -m and -W options
From: |
Richard W.M. Jones |
Subject: |
Re: [Qemu-devel] Effect of qemu-img convert -m and -W options |
Date: |
Thu, 16 Nov 2017 15:10:32 +0000 |
User-agent: |
Mutt/1.5.20 (2009-12-10) |
On Thu, Nov 16, 2017 at 02:47:46PM +0000, Stefan Hajnoczi wrote:
> The threads you observed are the thread pool that performs
> preadv(2)/pwritev(2) syscalls. The Linux AIO API could be used instead
> and does not use threads for read and write operations.
I guess if I used AIO then I wouldn't get any parallelism at all since
Linux doesn't block on local file access (at least, it never used to)?
> Interesting. Did you perform multiple runs of each setting to verify
> that the benchmark results are stable with little volatility?
I retested the -m 8 no-W/-W ones because those were so unexpected and
those are repeatable.
> Which command-line did you use to create the preallocated qcow2 file?
What I actually did was qemu-img convert -n into the existing qcow2
file, so there was no separate command for that.
> Are the source and target files on the same file system and host block
> device? The benefit of using multiple coroutines depends on the
> performance characteristics of the source and target files.
Both local filesystems, but on different SATA devices.
Rich.
--
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