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Re: [Qemu-block] [Qemu-stable] [PATCH v5 3/8] mirror: Do zero write on t
From: |
Fam Zheng |
Subject: |
Re: [Qemu-block] [Qemu-stable] [PATCH v5 3/8] mirror: Do zero write on target if sectors not allocated |
Date: |
Tue, 26 May 2015 14:07:23 +0800 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Tue, 05/26 07:53, Peter Lieven wrote:
> Am 26.05.2015 um 05:36 schrieb Fam Zheng:
> >If guest discards a source cluster, mirroring with bdrv_aio_readv is
> >overkill.
> >Some protocols do zero upon discard, where it's best to use
> >bdrv_aio_write_zeroes, otherwise, bdrv_aio_discard will be enough.
> >
> >Signed-off-by: Fam Zheng <address@hidden>
> >---
> > block/mirror.c | 20 ++++++++++++++++++--
> > 1 file changed, 18 insertions(+), 2 deletions(-)
> >
> >diff --git a/block/mirror.c b/block/mirror.c
> >index 85995b2..ba33254 100644
> >--- a/block/mirror.c
> >+++ b/block/mirror.c
> >@@ -164,6 +164,8 @@ static uint64_t coroutine_fn
> >mirror_iteration(MirrorBlockJob *s)
> > int64_t end, sector_num, next_chunk, next_sector, hbitmap_next_sector;
> > uint64_t delay_ns = 0;
> > MirrorOp *op;
> >+ int pnum;
> >+ int64_t ret;
> > s->sector_num = hbitmap_iter_next(&s->hbi);
> > if (s->sector_num < 0) {
> >@@ -290,8 +292,22 @@ static uint64_t coroutine_fn
> >mirror_iteration(MirrorBlockJob *s)
> > s->in_flight++;
> > s->sectors_in_flight += nb_sectors;
> > trace_mirror_one_iteration(s, sector_num, nb_sectors);
> >- bdrv_aio_readv(source, sector_num, &op->qiov, nb_sectors,
> >- mirror_read_complete, op);
> >+
> >+ ret = bdrv_get_block_status_above(source, NULL, sector_num,
> >+ nb_sectors, &pnum);
> >+ if (ret < 0 || pnum < nb_sectors ||
> >+ (ret & BDRV_BLOCK_DATA && !(ret & BDRV_BLOCK_ZERO))) {
> >+ bdrv_aio_readv(source, sector_num, &op->qiov, nb_sectors,
> >+ mirror_read_complete, op);
> >+ } else if (ret & BDRV_BLOCK_ZERO) {
> >+ bdrv_aio_write_zeroes(s->target, sector_num, op->nb_sectors,
> >+ s->unmap ? BDRV_REQ_MAY_UNMAP : 0,
> >+ mirror_write_complete, op);
> >+ } else {
> >+ assert(!(ret & BDRV_BLOCK_DATA));
> >+ bdrv_aio_discard(s->target, sector_num, op->nb_sectors,
> >+ mirror_write_complete, op);
> >+ }
>
> I wonder what happens if on the destination the discard is a NOP which is
> legal (at least in SCSI).
> In this case we might end up having different contents and source and
> destination. Or is this
> not a problem?
This is not a problem, because the guest already doesn't care about the
content.
Fam
- [Qemu-block] [PATCH v5 0/8] block: Mirror discarded sectors, Fam Zheng, 2015/05/25
- [Qemu-block] [PATCH v5 1/8] block: Add bdrv_get_block_status_above, Fam Zheng, 2015/05/25
- [Qemu-block] [PATCH v5 2/8] qmp: Add optional bool "unmap" to drive-mirror, Fam Zheng, 2015/05/25
- [Qemu-block] [PATCH v5 3/8] mirror: Do zero write on target if sectors not allocated, Fam Zheng, 2015/05/25
- [Qemu-block] [PATCH v5 4/8] block: Fix dirty bitmap in bdrv_co_discard, Fam Zheng, 2015/05/25
- [Qemu-block] [PATCH v5 5/8] block: Remove bdrv_reset_dirty, Fam Zheng, 2015/05/25
- [Qemu-block] [PATCH v5 6/8] qemu-iotests: Make block job methods common, Fam Zheng, 2015/05/25
- [Qemu-block] [PATCH v5 7/8] qemu-iotests: Add test case for mirror with unmap, Fam Zheng, 2015/05/25
- [Qemu-block] [PATCH v5 8/8] iotests: Use event_wait in wait_ready, Fam Zheng, 2015/05/25