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authorStefan Hajnoczi <stefanha@redhat.com>2021-12-07 13:23:31 +0000
committerStefan Hajnoczi <stefanha@redhat.com>2022-01-12 17:09:39 +0000
commit826cc32423db2a99d184dbf4f507c737d7e7a4ae (patch)
tree46947023e78c75098c2d50c0fec5eba1b365d296 /block/linux-aio.c
parent91f5f7a5df1fda8c34677a7c49ee8a4bb5b56a36 (diff)
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aio-posix: split poll check from ready handler
Adaptive polling measures the execution time of the polling check plus handlers called when a polled event becomes ready. Handlers can take a significant amount of time, making it look like polling was running for a long time when in fact the event handler was running for a long time. For example, on Linux the io_submit(2) syscall invoked when a virtio-blk device's virtqueue becomes ready can take 10s of microseconds. This can exceed the default polling interval (32 microseconds) and cause adaptive polling to stop polling. By excluding the handler's execution time from the polling check we make the adaptive polling calculation more accurate. As a result, the event loop now stays in polling mode where previously it would have fallen back to file descriptor monitoring. The following data was collected with virtio-blk num-queues=2 event_idx=off using an IOThread. Before: 168k IOPS, IOThread syscalls: 9837.115 ( 0.020 ms): IO iothread1/620155 io_submit(ctx_id: 140512552468480, nr: 16, iocbpp: 0x7fcb9f937db0) = 16 9837.158 ( 0.002 ms): IO iothread1/620155 write(fd: 103, buf: 0x556a2ef71b88, count: 8) = 8 9837.161 ( 0.001 ms): IO iothread1/620155 write(fd: 104, buf: 0x556a2ef71b88, count: 8) = 8 9837.163 ( 0.001 ms): IO iothread1/620155 ppoll(ufds: 0x7fcb90002800, nfds: 4, tsp: 0x7fcb9f1342d0, sigsetsize: 8) = 3 9837.164 ( 0.001 ms): IO iothread1/620155 read(fd: 107, buf: 0x7fcb9f939cc0, count: 512) = 8 9837.174 ( 0.001 ms): IO iothread1/620155 read(fd: 105, buf: 0x7fcb9f939cc0, count: 512) = 8 9837.176 ( 0.001 ms): IO iothread1/620155 read(fd: 106, buf: 0x7fcb9f939cc0, count: 512) = 8 9837.209 ( 0.035 ms): IO iothread1/620155 io_submit(ctx_id: 140512552468480, nr: 32, iocbpp: 0x7fca7d0cebe0) = 32 174k IOPS (+3.6%), IOThread syscalls: 9809.566 ( 0.036 ms): IO iothread1/623061 io_submit(ctx_id: 140539805028352, nr: 32, iocbpp: 0x7fd0cdd62be0) = 32 9809.625 ( 0.001 ms): IO iothread1/623061 write(fd: 103, buf: 0x5647cfba5f58, count: 8) = 8 9809.627 ( 0.002 ms): IO iothread1/623061 write(fd: 104, buf: 0x5647cfba5f58, count: 8) = 8 9809.663 ( 0.036 ms): IO iothread1/623061 io_submit(ctx_id: 140539805028352, nr: 32, iocbpp: 0x7fd0d0388b50) = 32 Notice that ppoll(2) and eventfd read(2) syscalls are eliminated because the IOThread stays in polling mode instead of falling back to file descriptor monitoring. As usual, polling is not implemented on Windows so this patch ignores the new io_poll_read() callback in aio-win32.c. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Stefano Garzarella <sgarzare@redhat.com> Message-id: 20211207132336.36627-2-stefanha@redhat.com [Fixed up aio_set_event_notifier() calls in tests/unit/test-fdmon-epoll.c added after this series was queued. --Stefan] Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'block/linux-aio.c')
-rw-r--r--block/linux-aio.c16
1 files changed, 10 insertions, 6 deletions
diff --git a/block/linux-aio.c b/block/linux-aio.c
index f53ae72..4c423fc 100644
--- a/block/linux-aio.c
+++ b/block/linux-aio.c
@@ -263,12 +263,15 @@ static bool qemu_laio_poll_cb(void *opaque)
LinuxAioState *s = container_of(e, LinuxAioState, e);
struct io_event *events;
- if (!io_getevents_peek(s->ctx, &events)) {
- return false;
- }
+ return io_getevents_peek(s->ctx, &events);
+}
+
+static void qemu_laio_poll_ready(EventNotifier *opaque)
+{
+ EventNotifier *e = opaque;
+ LinuxAioState *s = container_of(e, LinuxAioState, e);
qemu_laio_process_completions_and_submit(s);
- return true;
}
static void ioq_init(LaioQueue *io_q)
@@ -427,7 +430,7 @@ int coroutine_fn laio_co_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
void laio_detach_aio_context(LinuxAioState *s, AioContext *old_context)
{
- aio_set_event_notifier(old_context, &s->e, false, NULL, NULL);
+ aio_set_event_notifier(old_context, &s->e, false, NULL, NULL, NULL);
qemu_bh_delete(s->completion_bh);
s->aio_context = NULL;
}
@@ -438,7 +441,8 @@ void laio_attach_aio_context(LinuxAioState *s, AioContext *new_context)
s->completion_bh = aio_bh_new(new_context, qemu_laio_completion_bh, s);
aio_set_event_notifier(new_context, &s->e, false,
qemu_laio_completion_cb,
- qemu_laio_poll_cb);
+ qemu_laio_poll_cb,
+ qemu_laio_poll_ready);
}
LinuxAioState *laio_init(Error **errp)