On Wed, Jul 13, 2016 at 09:57:09AM +0200, Roman Pen wrote: Please send each new revision of a patch series as a separate email thread. Do not thread revisions with Reply-To:, References:.
See http://qemu-project.org/Contribute/SubmitAPatch for all the guidelines on submitting patches. > v1..v2: > > o comment tweaks. > o fix QEMU coding style. The changelog is useful for reviewers but is no longer useful once the patch has been merged. Therefore it goes below the '---' so that git-am(1) doesn't include it when merging. > Invoking io_setup(MAX_EVENTS) we ask kernel to create ring buffer for us > with specified number of events. But kernel ring buffer allocation logic > is a bit tricky (ring buffer is page size aligned + some percpu allocation > are required) so eventually more than requested events number is allocated. > > From a userspace side we have to follow the convention and should not try > to io_submit() more or logic, which consumes completed events, should be > changed accordingly. The pitfall is in the following sequence: > > MAX_EVENTS = 128 > io_setup(MAX_EVENTS) > > io_submit(MAX_EVENTS) > io_submit(MAX_EVENTS) > > /* now 256 events are in-flight */ > > io_getevents(MAX_EVENTS) = 128 > > /* we can handle only 128 events at once, to be sure > * that nothing is pended the io_getevents(MAX_EVENTS) > * call must be invoked once more or hang will happen. */ > > To prevent the hang or reiteration of io_getevents() call this patch > restricts the number of in-flights, which is now limited to MAX_EVENTS. > > Signed-off-by: Roman Pen <roman.peny...@profitbricks.com> > Reviewed-by: Fam Zheng <f...@redhat.com> > Cc: Stefan Hajnoczi <stefa...@redhat.com> > Cc: Paolo Bonzini <pbonz...@redhat.com> > Cc: qemu-devel@nongnu.org > --- > block/linux-aio.c | 26 ++++++++++++++++---------- > 1 file changed, 16 insertions(+), 10 deletions(-) > > diff --git a/block/linux-aio.c b/block/linux-aio.c > index e468960..78f4524 100644 > --- a/block/linux-aio.c > +++ b/block/linux-aio.c > @@ -28,8 +28,6 @@ > */ > #define MAX_EVENTS 128 > > -#define MAX_QUEUED_IO 128 > - > struct qemu_laiocb { > BlockAIOCB common; > Coroutine *co; > @@ -44,7 +42,8 @@ struct qemu_laiocb { > > typedef struct { > int plugged; > - unsigned int n; > + unsigned int in_queue; > + unsigned int in_flight; > bool blocked; > QSIMPLEQ_HEAD(, qemu_laiocb) pending; > } LaioQueue; > @@ -129,6 +128,7 @@ static void qemu_laio_completion_bh(void *opaque) > s->event_max = 0; > return; /* no more events */ > } > + s->io_q.in_flight -= s->event_max; > } > > /* Reschedule so nested event loops see currently pending completions */ > @@ -190,7 +190,8 @@ static void ioq_init(LaioQueue *io_q) > { > QSIMPLEQ_INIT(&io_q->pending); > io_q->plugged = 0; > - io_q->n = 0; > + io_q->in_queue = 0; > + io_q->in_flight = 0; > io_q->blocked = false; > } > > @@ -198,14 +199,17 @@ static void ioq_submit(LinuxAioState *s) > { > int ret, len; > struct qemu_laiocb *aiocb; > - struct iocb *iocbs[MAX_QUEUED_IO]; > + struct iocb *iocbs[MAX_EVENTS]; > QSIMPLEQ_HEAD(, qemu_laiocb) completed; > > do { > + if (s->io_q.in_flight >= MAX_EVENTS) { > + break; > + } > len = 0; > QSIMPLEQ_FOREACH(aiocb, &s->io_q.pending, next) { > iocbs[len++] = &aiocb->iocb; > - if (len == MAX_QUEUED_IO) { > + if (s->io_q.in_flight + len >= MAX_EVENTS) { > break; > } > } > @@ -218,11 +222,12 @@ static void ioq_submit(LinuxAioState *s) > abort(); > } > > - s->io_q.n -= ret; > + s->io_q.in_flight += ret; > + s->io_q.in_queue -= ret; > aiocb = container_of(iocbs[ret - 1], struct qemu_laiocb, iocb); > QSIMPLEQ_SPLIT_AFTER(&s->io_q.pending, aiocb, next, &completed); > } while (ret == len && !QSIMPLEQ_EMPTY(&s->io_q.pending)); > - s->io_q.blocked = (s->io_q.n > 0); > + s->io_q.blocked = (s->io_q.in_queue > 0); > } > > void laio_io_plug(BlockDriverState *bs, LinuxAioState *s) > @@ -263,9 +268,10 @@ static int laio_do_submit(int fd, struct qemu_laiocb > *laiocb, off_t offset, > io_set_eventfd(&laiocb->iocb, event_notifier_get_fd(&s->e)); > > QSIMPLEQ_INSERT_TAIL(&s->io_q.pending, laiocb, next); > - s->io_q.n++; > + s->io_q.in_queue++; > if (!s->io_q.blocked && > - (!s->io_q.plugged || s->io_q.n >= MAX_QUEUED_IO)) { > + (!s->io_q.plugged || > + s->io_q.in_flight + s->io_q.in_queue >= MAX_EVENTS)) { > ioq_submit(s); > } > > -- > 2.8.2 > >
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