motorhead/qemu
1
0
Fork 0
mirror of https://github.com/Motorhead1991/qemu.git synced 2025-08-02 23:33:54 -06:00
Code Issues Projects Releases Packages Wiki Activity Actions

virtio: use defer_call() in virtio_irqfd_notify()

Browse source 
virtio-blk and virtio-scsi invoke virtio_irqfd_notify() to send Used
Buffer Notifications from an IOThread. This involves an eventfd
write(2) syscall. Calling this repeatedly when completing multiple I/O
requests in a row is wasteful.

Use the defer_call() API to batch together virtio_irqfd_notify() calls
made during thread pool (aio=threads), Linux AIO (aio=native), and
io_uring (aio=io_uring) completion processing.

Behavior is unchanged for emulated devices that do not use
defer_call_begin()/defer_call_end() since defer_call() immediately
invokes the callback when called outside a
defer_call_begin()/defer_call_end() region.

fio rw=randread bs=4k iodepth=64 numjobs=8 IOPS increases by ~9% with a
single IOThread and 8 vCPUs. iodepth=1 decreases by ~1% but this could
be noise. Detailed performance data and configuration specifics are
available here:
https://gitlab.com/stefanha/virt-playbooks/-/tree/blk_io_plug-irqfd

This duplicates the BH that virtio-blk uses for batching. The next
commit will remove it.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20230913200045.1024233-4-stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2023-09-13 16:00:44 -04:00 • committed by Kevin Wolf
parent 433fcea40c
commit 84d61e5f36
5 changed files with 28 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

5
util/thread-pool.c
View file

@ -15,6 +15,7 @@
* GNU GPL, version 2 or (at your option) any later version.
*/
#include "qemu/osdep.h"
#include "qemu/defer-call.h"
#include "qemu/queue.h"
#include "qemu/thread.h"
#include "qemu/coroutine.h"
@ -175,6 +176,8 @@ static void thread_pool_completion_bh(void *opaque)
ThreadPool *pool = opaque;
ThreadPoolElement *elem, *next;
defer_call_begin(); /* cb() may use defer_call() to coalesce work */
restart:
QLIST_FOREACH_SAFE(elem, &pool->head, all, next) {
if (elem->state != THREAD_DONE) {
@ -208,6 +211,8 @@ restart:
qemu_aio_unref(elem);
}
}
defer_call_end();
}
static void thread_pool_cancel(BlockAIOCB *acb)