Message ID | 1465837535-30067-16-git-send-email-stefanha@redhat.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
On 13/06/2016 19:05, Stefan Hajnoczi wrote: > index 80fd3c7..046e95c 100644 > --- a/block/mirror.c > +++ b/block/mirror.c > @@ -331,6 +331,8 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s) > mirror_wait_for_io(s); > } > > + block_job_pause_point(&s->common); I/O can be in-flight here, so your description of the function is not 100% accurate. I suppose it's okay because s->waiting_for_io is false at the pause points you specified? I guess a comment that explains it will do; and apart from this detail, the patches are really nice. Or maybe it's just that you scared with that 00/15 in the cover letter. :-> Paolo > cnt = bdrv_get_dirty_count(s->dirty_bitmap); > /* s->common.offset contains the number of bytes already processed so > * far, cnt is the number of dirty sectors remaining and > @@ -781,18 +787,38 @@ static void mirror_complete(BlockJob *job, Error **errp) > block_job_enter(&s->common); > }
On Tue, Jun 14, 2016 at 1:09 PM, Paolo Bonzini <pbonzini@redhat.com> wrote: > On 13/06/2016 19:05, Stefan Hajnoczi wrote: >> index 80fd3c7..046e95c 100644 >> --- a/block/mirror.c >> +++ b/block/mirror.c >> @@ -331,6 +331,8 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s) >> mirror_wait_for_io(s); >> } >> >> + block_job_pause_point(&s->common); > > I/O can be in-flight here, so your description of the function is not > 100% accurate. I suppose it's okay because s->waiting_for_io is false > at the pause points you specified? You are right, this brings up a subtle issue that already exists without my patches: The co-routine may sleep with aio requests pending. This makes the job "paused" (!job->busy) while there is still activity! The solution for AioContext switching that this patch relies on is: +static void mirror_detach_aio_context(BlockJob *job) +{ + MirrorBlockJob *s = container_of(job, MirrorBlockJob, common); + + while (s->in_flight > 0) { + aio_poll(blk_get_aio_context(job->blk), true); + } +} blockjob.c:block_job_detach_aio_context() first calls block_job_pause(), then mirror_detach_aio_context() above, and finally waits for !job->busy. I chose this approach because it safely handles existing sleep or block_job_yield() callers while there is still activity. Now that I think more about it, we should solve the problem not just for AioContext switching but also for pausing sleeping or block_job_yield() coroutines. I'll try to come up with a solution in v4. Stefan
diff --git a/block/mirror.c b/block/mirror.c index 80fd3c7..046e95c 100644 --- a/block/mirror.c +++ b/block/mirror.c @@ -331,6 +331,8 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s) mirror_wait_for_io(s); } + block_job_pause_point(&s->common); + /* Find the number of consective dirty chunks following the first dirty * one, and wait for in flight requests in them. */ while (nb_chunks * sectors_per_chunk < (s->buf_size >> BDRV_SECTOR_BITS)) { @@ -581,6 +583,8 @@ static void coroutine_fn mirror_run(void *opaque) if (now - last_pause_ns > SLICE_TIME) { last_pause_ns = now; block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, 0); + } else { + block_job_pause_point(&s->common); } if (block_job_is_cancelled(&s->common)) { @@ -612,6 +616,8 @@ static void coroutine_fn mirror_run(void *opaque) goto immediate_exit; } + block_job_pause_point(&s->common); + cnt = bdrv_get_dirty_count(s->dirty_bitmap); /* s->common.offset contains the number of bytes already processed so * far, cnt is the number of dirty sectors remaining and @@ -781,18 +787,38 @@ static void mirror_complete(BlockJob *job, Error **errp) block_job_enter(&s->common); } +static void mirror_attached_aio_context(BlockJob *job, AioContext *new_context) +{ + MirrorBlockJob *s = container_of(job, MirrorBlockJob, common); + + blk_set_aio_context(s->target, new_context); +} + +static void mirror_detach_aio_context(BlockJob *job) +{ + MirrorBlockJob *s = container_of(job, MirrorBlockJob, common); + + while (s->in_flight > 0) { + aio_poll(blk_get_aio_context(job->blk), true); + } +} + static const BlockJobDriver mirror_job_driver = { - .instance_size = sizeof(MirrorBlockJob), - .job_type = BLOCK_JOB_TYPE_MIRROR, - .set_speed = mirror_set_speed, - .complete = mirror_complete, + .instance_size = sizeof(MirrorBlockJob), + .job_type = BLOCK_JOB_TYPE_MIRROR, + .set_speed = mirror_set_speed, + .complete = mirror_complete, + .attached_aio_context = mirror_attached_aio_context, + .detach_aio_context = mirror_detach_aio_context, }; static const BlockJobDriver commit_active_job_driver = { - .instance_size = sizeof(MirrorBlockJob), - .job_type = BLOCK_JOB_TYPE_COMMIT, - .set_speed = mirror_set_speed, - .complete = mirror_complete, + .instance_size = sizeof(MirrorBlockJob), + .job_type = BLOCK_JOB_TYPE_COMMIT, + .set_speed = mirror_set_speed, + .complete = mirror_complete, + .attached_aio_context = mirror_attached_aio_context, + .detach_aio_context = mirror_detach_aio_context, }; static void mirror_start_job(BlockDriverState *bs, BlockDriverState *target,