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Re: [Qemu-devel] [PATCH] block/mirror: Sleep periodically during bitmap
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH] block/mirror: Sleep periodically during bitmap scanning |
Date: |
Wed, 13 May 2015 14:40:43 +0800 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Wed, 05/13 13:17, Wen Congyang wrote:
> On 05/13/2015 11:11 AM, Fam Zheng wrote:
> > Before, we only yield after initializing dirty bitmap, where the QMP
> > command would return. That may take very long, and guest IO will be
> > blocked.
>
> Do you have such case to reproduce it? If the disk image is too larger,
> and I think qemu doesn't cache all metedata in the memory. So we will
> yield in bdrv_is_allocated_above() when we read the metedata from the
> disk.
True for qcow2, but raw-posix has no such yield points, because it uses
lseek(..., SEEK_HOLE). I do have a reproducer - just try a big raw image on
your ext4.
Fam
>
> Thanks
> Wen Congyang
>
> >
> > Add sleep points like the later mirror iterations.
> >
> > Signed-off-by: Fam Zheng <address@hidden>
> > ---
> > block/mirror.c | 13 ++++++++++++-
> > 1 file changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/block/mirror.c b/block/mirror.c
> > index 1a1d997..baed225 100644
> > --- a/block/mirror.c
> > +++ b/block/mirror.c
> > @@ -467,11 +467,23 @@ static void coroutine_fn mirror_run(void *opaque)
> > sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
> > mirror_free_init(s);
> >
> > + last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
> > if (!s->is_none_mode) {
> > /* First part, loop on the sectors and initialize the dirty
> > bitmap. */
> > BlockDriverState *base = s->base;
> > for (sector_num = 0; sector_num < end; ) {
> > int64_t next = (sector_num | (sectors_per_chunk - 1)) + 1;
> > + int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
> > +
> > + if (now - last_pause_ns > SLICE_TIME) {
> > + last_pause_ns = now;
> > + block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, 0);
> > + }
> > +
> > + if (block_job_is_cancelled(&s->common)) {
> > + goto immediate_exit;
> > + }
> > +
> > ret = bdrv_is_allocated_above(bs, base,
> > sector_num, next - sector_num,
> > &n);
> >
> > @@ -490,7 +502,6 @@ static void coroutine_fn mirror_run(void *opaque)
> > }
> >
> > bdrv_dirty_iter_init(s->dirty_bitmap, &s->hbi);
> > - last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
> > for (;;) {
> > uint64_t delay_ns = 0;
> > int64_t cnt;
> >
>