Commit d42cf288 authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Fam Zheng
Browse files

block: change drain to look only at one child at a time 



bdrv_requests_pending is checking children to also wait until internal
requests (such as metadata writes) have completed.  However, checking
children is in general overkill.  Children requests can be of two kinds:

- requests caused by an operation on bs, e.g. a bdrv_aio_write to bs
causing a write to bs->file->bs.  In this case, the parent's in_flight
count will always be incremented by at least one for every request in
the child.

- asynchronous metadata writes or flushes.  Such writes can be started
even if bs's in_flight count is zero, but not after the .bdrv_drain
callback has been invoked.

This patch therefore changes bdrv_drain to finish I/O in the parent
(after which the parent's in_flight will be locked to zero), call
bdrv_drain (after which the parent will not generate I/O on the child
anymore), and then wait for internal I/O in the children to complete.

Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: default avatarFam Zheng <famz@redhat.com>
Message-Id: <1477565348-5458-6-git-send-email-pbonzini@redhat.com>
Signed-off-by: default avatarFam Zheng <famz@redhat.com>
parent 99723548

block/io.c

+26 −21
Original line number Diff line number Diff line
@@ -156,16 +156,33 @@ bool bdrv_requests_pending(BlockDriverState *bs) 
    return false;

}



static void bdrv_drain_recurse(BlockDriverState *bs)

static bool bdrv_drain_poll(BlockDriverState *bs)

{

    bool waited = false;



    while (atomic_read(&bs->in_flight) > 0) {

        aio_poll(bdrv_get_aio_context(bs), true);

        waited = true;

    }

    return waited;

}



static bool bdrv_drain_recurse(BlockDriverState *bs)

{

    BdrvChild *child;

    bool waited;



    waited = bdrv_drain_poll(bs);



    if (bs->drv && bs->drv->bdrv_drain) {

        bs->drv->bdrv_drain(bs);

    }



    QLIST_FOREACH(child, &bs->children, next) {

        bdrv_drain_recurse(child->bs);

        waited |= bdrv_drain_recurse(child->bs);

    }



    return waited;

}



typedef struct {
@@ -174,14 +191,6 @@ typedef struct { 
    bool done;

} BdrvCoDrainData;



static void bdrv_drain_poll(BlockDriverState *bs)

{

    while (bdrv_requests_pending(bs)) {

        /* Keep iterating */

        aio_poll(bdrv_get_aio_context(bs), true);

    }

}



static void bdrv_co_drain_bh_cb(void *opaque)

{

    BdrvCoDrainData *data = opaque;
@@ -189,7 +198,7 @@ static void bdrv_co_drain_bh_cb(void *opaque) 
    BlockDriverState *bs = data->bs;



    bdrv_dec_in_flight(bs);

    bdrv_drain_poll(bs);

    bdrv_drained_begin(bs);

    data->done = true;

    qemu_coroutine_enter(co);

}
@@ -220,6 +229,11 @@ static void coroutine_fn bdrv_co_yield_to_drain(BlockDriverState *bs) 


void bdrv_drained_begin(BlockDriverState *bs)

{

    if (qemu_in_coroutine()) {

        bdrv_co_yield_to_drain(bs);

        return;

    }



    if (!bs->quiesce_counter++) {

        aio_disable_external(bdrv_get_aio_context(bs));

        bdrv_parent_drained_begin(bs);
@@ -227,11 +241,6 @@ void bdrv_drained_begin(BlockDriverState *bs) 


    bdrv_io_unplugged_begin(bs);

    bdrv_drain_recurse(bs);

    if (qemu_in_coroutine()) {

        bdrv_co_yield_to_drain(bs);

    } else {

        bdrv_drain_poll(bs);

    }

    bdrv_io_unplugged_end(bs);

}
@@ -299,7 +308,6 @@ void bdrv_drain_all(void) 
        aio_context_acquire(aio_context);

        bdrv_parent_drained_begin(bs);

        bdrv_io_unplugged_begin(bs);

        bdrv_drain_recurse(bs);

        aio_context_release(aio_context);



        if (!g_slist_find(aio_ctxs, aio_context)) {
@@ -322,10 +330,7 @@ void bdrv_drain_all(void) 
            aio_context_acquire(aio_context);

            for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {

                if (aio_context == bdrv_get_aio_context(bs)) {

                    if (bdrv_requests_pending(bs)) {

                        aio_poll(aio_context, true);

                        waited = true;

                    }

                    waited |= bdrv_drain_recurse(bs);

                }

            }

            aio_context_release(aio_context);