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Stefano Garzarella d7ddd0a161 linux-aio: limit the batch size using aio-max-batch parameter 
When there are multiple queues attached to the same AIO context,
some requests may experience high latency, since in the worst case
the AIO engine queue is only flushed when it is full (MAX_EVENTS) or
there are no more queues plugged.

Commit 2558cb8dd4 ("linux-aio: increasing MAX_EVENTS to a larger
hardcoded value") changed MAX_EVENTS from 128 to 1024, to increase
the number of in-flight requests. But this change also increased
the potential maximum batch to 1024 elements.

When there is a single queue attached to the AIO context, the issue
is mitigated from laio_io_unplug() that will flush the queue every
time is invoked since there can't be others queue plugged.

Let's use the new `aio-max-batch` IOThread parameter to mitigate
this issue, limiting the number of requests in a batch.

We also define a default value (32): this value is obtained running
some benchmarks and it represents a good tradeoff between the latency
increase while a request is queued and the cost of the io_submit(2)
system call.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-id: 20210721094211.69853-4-sgarzare@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2021-07-21 13:47:50 +01:00
..
export block/export: Conditionally ignore set-context error 2021-07-20 16:49:31 +02:00
monitor monitor: hmp_qemu_io: acquire aio contex, fix crash 2021-05-14 16:14:10 +02:00
accounting.c
aio_task.c
amend.c
backup-top.c block/backup-top: drop .active 2021-04-30 12:27:48 +02:00
backup-top.h
backup.c mirror: stop cancelling in-flight requests on non-force cancel in READY 2021-05-14 16:14:10 +02:00
blkdebug.c blkdebug: protect rules and suspended_reqs with a lock 2021-07-19 17:38:38 +02:00
blklogwrites.c block: check return value of bdrv_open_child and drop error propagation 2021-03-08 15:07:09 -06:00
blkreplay.c block: check return value of bdrv_open_child and drop error propagation 2021-03-08 15:07:09 -06:00
blkverify.c block: check return value of bdrv_open_child and drop error propagation 2021-03-08 15:07:09 -06:00
block-backend.c block: add max_hw_transfer to BlockLimits 2021-06-25 10:54:13 +02:00
block-copy.c block-copy: atomic .cancelled and .finished fields in BlockCopyCallState 2021-06-25 14:33:51 +03:00
block-gen.h
bochs.c
cloop.c
commit.c block/commit: use QEMU_AUTO_VFREE 2021-06-29 16:51:21 +02:00
copy-on-read.c block/copy-on-read: use bdrv_drop_filter() and drop s->active 2021-05-14 16:14:10 +02:00
copy-on-read.h
coroutines.h block/nbd: reuse nbd_co_do_establish_connection() in nbd_open() 2021-06-18 12:21:22 -05:00
create.c
crypto.c block: add bdrv_co_delete_file_noerr 2021-02-15 15:10:14 +01:00
crypto.h
curl.c curl: Disconnect sockets from CURLState 2021-03-19 10:15:06 +01:00
dirty-bitmap.c block: remove dirty bitmaps 'status' field 2021-03-18 09:22:55 +00:00
dmg-bz2.c
dmg-lzfse.c
dmg.c
dmg.h
file-posix.c block/file-posix: Optimize for macOS 2021-07-06 14:28:55 +01:00
file-win32.c
filter-compress.c
gluster.c qapi: More complex uses of QAPI_LIST_APPEND 2021-01-28 08:08:45 +01:00
io_uring.c
io.c block/io: Merge discard request alignments 2021-07-06 14:28:55 +01:00
iscsi-opts.c modules: add block module annotations 2021-07-09 18:20:27 +02:00
iscsi.c
linux-aio.c linux-aio: limit the batch size using aio-max-batch parameter 2021-07-21 13:47:50 +01:00
meson.build meson: fix missing preprocessor symbols 2021-07-09 18:19:00 +02:00
mirror.c block/mirror: fix active mirror dead-lock in mirror_wait_on_conflicts 2021-07-20 13:14:45 +02:00
nbd.c nbd: register yank function earlier 2021-07-12 11:24:00 -05:00
nfs.c util/uri: do not check argument of uri_free() 2021-07-09 12:26:05 +02:00
null.c
nvme.c block/nvme: Trace NVMe spec version supported by the controller 2021-02-02 17:05:38 +01:00
parallels-ext.c parallels: support bitmap extension for read-only mode 2021-03-08 14:56:55 +01:00
parallels.c parallels: support bitmap extension for read-only mode 2021-03-08 14:56:55 +01:00
parallels.h parallels: support bitmap extension for read-only mode 2021-03-08 14:56:55 +01:00
preallocate.c
progress_meter.c progressmeter: protect with a mutex 2021-06-25 14:24:24 +03:00
qapi-sysemu.c
qapi.c block: use GDateTime for formatting timestamp when dumping snapshot info 2021-06-14 13:28:50 +01:00
qcow2-bitmap.c nbd patches for 2021-03-09 2021-03-11 13:57:08 +00:00
qcow2-cache.c
qcow2-cluster.c
qcow2-refcount.c
qcow2-snapshot.c block: consistently use bdrv_is_read_only() 2021-06-02 14:23:20 +02:00
qcow2-threads.c
qcow2.c qcow2: Fix dangling pointer after reopen for 'file' 2021-07-09 13:19:11 +02:00
qcow2.h block/qcow2-bitmap: return status from qcow2_store_persistent_dirty_bitmaps 2021-03-08 16:03:21 -06:00
qcow.c
qed-check.c
qed-cluster.c
qed-l2-cache.c
qed-table.c
qed.c block/qed: bdrv_qed_do_open: deal with errp 2021-03-08 16:03:32 -06:00
qed.h
quorum.c block/quorum: Provide .bdrv_co_flush instead of .bdrv_co_flush_to_disk 2021-06-02 14:23:20 +02:00
raw-format.c block/raw-format: implement .bdrv_cancel_in_flight handler 2021-02-12 09:45:18 -06:00
rbd.c block/rbd: fix type of task->complete 2021-07-09 12:26:05 +02:00
replication.c replication: Remove workaround 2021-07-20 16:11:53 +02:00
snapshot.c block/snapshot: Clarify goto fallback behavior 2021-06-24 09:49:04 +02:00
ssh.c util/uri: do not check argument of uri_free() 2021-07-09 12:26:05 +02:00
stream.c stream: Don't crash when node permission is denied 2021-03-19 10:15:06 +01:00
throttle-groups.c block/throttle-groups: throttle_group_co_io_limits_intercept(): 64bit bytes 2021-02-03 08:14:00 -06:00
throttle.c
trace-events block: add trace point when fdatasync fails 2021-06-14 13:28:50 +01:00
trace.h
vdi.c block/vdi: Don't assume that blocks are larger than VdiHeader 2021-03-31 10:44:21 +01:00
vhdx-endian.c
vhdx-log.c block: consistently use bdrv_is_read_only() 2021-06-02 14:23:20 +02:00
vhdx.c
vhdx.h
vmdk.c qapi: Use QAPI_LIST_APPEND in trivial cases 2021-01-28 08:08:45 +01:00
vpc.c
vvfat.c block/vvfat: fix: drop backing 2021-07-20 16:30:20 +02:00
win32-aio.c
write-threshold.c write-threshold: deal with includes 2021-05-14 16:14:10 +02:00