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Re: [Qemu-devel] [PATCH 5/9] mirror: improve performance of mirroring of
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH 5/9] mirror: improve performance of mirroring of empty disk |
Date: |
Fri, 17 Jun 2016 14:56:38 +0100 |
User-agent: |
Mutt/1.6.1 (2016-04-27) |
On Thu, Jun 16, 2016 at 08:53:12PM -0600, Eric Blake wrote:
> On 06/16/2016 04:10 AM, Stefan Hajnoczi wrote:
>
> >
> > io_sectors currently only accounts for bytes written, not bytes read.
> >
> > Therefore, I think we need:
> >
> > /* Don't charge for efficient zero writes */
> > if (drv->bdrv_co_pwrite_zeroes) {
> > io_sectors = 0;
> > }
>
> That's not sufficient. NBD will have conditional support for write
> zeroes, depending on whether the server supports it (that is, once my
> patches for NBD_CMD_WRITE_ZEROES get out of a holding pattern on all the
> other patches in the queue being flushed...). So NBD will have the
> bdrv_co_pwrite_zeroes callback, but that doesn't mean it will always
> work - if the server doesn't support it, calling bdrv_co_pwrite_zeroes
> will fail with -ENOTSUP and fall back to less-efficient writes that need
> to be accounted for.
Good point! Optimizations are tricky :-).
Stefan
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- Re: [Qemu-devel] [PATCH 6/9] block: pass qiov into before_write notifier, (continued)
[Qemu-devel] [PATCH 9/9] mirror: replace bdrv_dirty_bitmap with plain hbitmap, Denis V. Lunev, 2016/06/14
[Qemu-devel] [PATCH 8/9] mirror: use synch scheme for drive mirror, Denis V. Lunev, 2016/06/14
Re: [Qemu-devel] [PATCH 0/9] major rework of drive-mirror, Kevin Wolf, 2016/06/15
Re: [Qemu-devel] [PATCH 0/9] major rework of drive-mirror, Stefan Hajnoczi, 2016/06/15