[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-block] [Qemu-devel] [PATCH 5/9] mirror: improve performance of

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH 5/9] mirror: improve performance of mirroring of empty disk
Date: Thu, 16 Jun 2016 20:53:12 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0

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.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

Attachment: signature.asc
Description: OpenPGP digital signature

reply via email to

[Prev in Thread] Current Thread [Next in Thread]