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block/linux-aio: convert to blk_io_plug_call() API 
Stop using the .bdrv_co_io_plug() API because it is not multi-queue
block layer friendly. Use the new blk_io_plug_call() API to batch I/O
submission instead.

Note that a dev_max_batch check is dropped in laio_io_unplug() because
the semantics of unplug_fn() are different from .bdrv_co_unplug():
1. unplug_fn() is only called when the last blk_io_unplug() call occurs,
   not every time blk_io_unplug() is called.
2. unplug_fn() is per-thread, not per-BlockDriverState, so there is no
   way to get per-BlockDriverState fields like dev_max_batch.

Therefore this condition cannot be moved to laio_unplug_fn(). It is not
obvious that this condition affects performance in practice, so I am
removing it instead of trying to come up with a more complex mechanism
to preserve the condition.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Acked-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-id: 20230530180959.1108766-6-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Stefan Hajnoczi committed Jun 1, 2023
1 parent 6a6da23 commit 0766828
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Showing 3 changed files with 11 additions and 65 deletions.
28 changes: 0 additions & 28 deletions block/file-posix.c
View file
Expand Up @@ -2550,26 +2550,6 @@ static int coroutine_fn raw_co_pwritev(BlockDriverState *bs, int64_t offset,
return raw_co_prw(bs, offset, bytes, qiov, QEMU_AIO_WRITE);
}

static void coroutine_fn raw_co_io_plug(BlockDriverState *bs)
{
BDRVRawState __attribute__((unused)) *s = bs->opaque;
#ifdef CONFIG_LINUX_AIO
if (s->use_linux_aio) {
laio_io_plug();
}
#endif
}

static void coroutine_fn raw_co_io_unplug(BlockDriverState *bs)
{
BDRVRawState __attribute__((unused)) *s = bs->opaque;
#ifdef CONFIG_LINUX_AIO
if (s->use_linux_aio) {
laio_io_unplug(s->aio_max_batch);
}
#endif
}

static int coroutine_fn raw_co_flush_to_disk(BlockDriverState *bs)
{
BDRVRawState *s = bs->opaque;
Expand Down Expand Up @@ -3914,8 +3894,6 @@ BlockDriver bdrv_file = {
.bdrv_co_copy_range_from = raw_co_copy_range_from,
.bdrv_co_copy_range_to = raw_co_copy_range_to,
.bdrv_refresh_limits = raw_refresh_limits,
.bdrv_co_io_plug = raw_co_io_plug,
.bdrv_co_io_unplug = raw_co_io_unplug,
.bdrv_attach_aio_context = raw_aio_attach_aio_context,

.bdrv_co_truncate = raw_co_truncate,
Expand Down Expand Up @@ -4286,8 +4264,6 @@ static BlockDriver bdrv_host_device = {
.bdrv_co_copy_range_from = raw_co_copy_range_from,
.bdrv_co_copy_range_to = raw_co_copy_range_to,
.bdrv_refresh_limits = raw_refresh_limits,
.bdrv_co_io_plug = raw_co_io_plug,
.bdrv_co_io_unplug = raw_co_io_unplug,
.bdrv_attach_aio_context = raw_aio_attach_aio_context,

.bdrv_co_truncate = raw_co_truncate,
Expand Down Expand Up @@ -4424,8 +4400,6 @@ static BlockDriver bdrv_host_cdrom = {
.bdrv_co_pwritev = raw_co_pwritev,
.bdrv_co_flush_to_disk = raw_co_flush_to_disk,
.bdrv_refresh_limits = cdrom_refresh_limits,
.bdrv_co_io_plug = raw_co_io_plug,
.bdrv_co_io_unplug = raw_co_io_unplug,
.bdrv_attach_aio_context = raw_aio_attach_aio_context,

.bdrv_co_truncate = raw_co_truncate,
Expand Down Expand Up @@ -4552,8 +4526,6 @@ static BlockDriver bdrv_host_cdrom = {
.bdrv_co_pwritev = raw_co_pwritev,
.bdrv_co_flush_to_disk = raw_co_flush_to_disk,
.bdrv_refresh_limits = cdrom_refresh_limits,
.bdrv_co_io_plug = raw_co_io_plug,
.bdrv_co_io_unplug = raw_co_io_unplug,
.bdrv_attach_aio_context = raw_aio_attach_aio_context,

.bdrv_co_truncate = raw_co_truncate,
Expand Down
41 changes: 11 additions & 30 deletions block/linux-aio.c
View file
Expand Up @@ -15,6 +15,7 @@
#include "qemu/event_notifier.h"
#include "qemu/coroutine.h"
#include "qapi/error.h"
#include "sysemu/block-backend.h"

/* Only used for assertions. */
#include "qemu/coroutine_int.h"
Expand Down Expand Up @@ -46,7 +47,6 @@ struct qemu_laiocb {
};

typedef struct {
int plugged;
unsigned int in_queue;
unsigned int in_flight;
bool blocked;
Expand Down Expand Up @@ -236,7 +236,7 @@ static void qemu_laio_process_completions_and_submit(LinuxAioState *s)
{
qemu_laio_process_completions(s);

if (!s->io_q.plugged && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
if (!QSIMPLEQ_EMPTY(&s->io_q.pending)) {
ioq_submit(s);
}
}
Expand Down Expand Up @@ -277,7 +277,6 @@ static void qemu_laio_poll_ready(EventNotifier *opaque)
static void ioq_init(LaioQueue *io_q)
{
QSIMPLEQ_INIT(&io_q->pending);
io_q->plugged = 0;
io_q->in_queue = 0;
io_q->in_flight = 0;
io_q->blocked = false;
Expand Down Expand Up @@ -354,31 +353,11 @@ static uint64_t laio_max_batch(LinuxAioState *s, uint64_t dev_max_batch)
return max_batch;
}

void laio_io_plug(void)
static void laio_unplug_fn(void *opaque)
{
AioContext *ctx = qemu_get_current_aio_context();
LinuxAioState *s = aio_get_linux_aio(ctx);

s->io_q.plugged++;
}

void laio_io_unplug(uint64_t dev_max_batch)
{
AioContext *ctx = qemu_get_current_aio_context();
LinuxAioState *s = aio_get_linux_aio(ctx);

assert(s->io_q.plugged);
s->io_q.plugged--;
LinuxAioState *s = opaque;

/*
* Why max batch checking is performed here:
* Another BDS may have queued requests with a higher dev_max_batch and
* therefore in_queue could now exceed our dev_max_batch. Re-check the max
* batch so we can honor our device's dev_max_batch.
*/
if (s->io_q.in_queue >= laio_max_batch(s, dev_max_batch) ||
(!s->io_q.plugged &&
!s->io_q.blocked && !QSIMPLEQ_EMPTY(&s->io_q.pending))) {
if (!s->io_q.blocked && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
ioq_submit(s);
}
}
Expand Down Expand Up @@ -410,10 +389,12 @@ static int laio_do_submit(int fd, struct qemu_laiocb *laiocb, off_t offset,

QSIMPLEQ_INSERT_TAIL(&s->io_q.pending, laiocb, next);
s->io_q.in_queue++;
if (!s->io_q.blocked &&
(!s->io_q.plugged ||
s->io_q.in_queue >= laio_max_batch(s, dev_max_batch))) {
ioq_submit(s);
if (!s->io_q.blocked) {
if (s->io_q.in_queue >= laio_max_batch(s, dev_max_batch)) {
ioq_submit(s);
} else {
blk_io_plug_call(laio_unplug_fn, s);
}
}

return 0;
Expand Down
7 changes: 0 additions & 7 deletions include/block/raw-aio.h
View file
Expand Up @@ -62,13 +62,6 @@ int coroutine_fn laio_co_submit(int fd, uint64_t offset, QEMUIOVector *qiov,

void laio_detach_aio_context(LinuxAioState *s, AioContext *old_context);
void laio_attach_aio_context(LinuxAioState *s, AioContext *new_context);

/*
* laio_io_plug/unplug work in the thread's current AioContext, therefore the
* caller must ensure that they are paired in the same IOThread.
*/
void laio_io_plug(void);
void laio_io_unplug(uint64_t dev_max_batch);
#endif
/* io_uring.c - Linux io_uring implementation */
#ifdef CONFIG_LINUX_IO_URING
Expand Down

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