qemu/migration
Stefan Hajnoczi 826cc32423 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>
2022-01-12 17:09:39 +00:00
..
block-dirty-bitmap.c migration: block-dirty-bitmap: add missing qemu_mutex_lock_iothread 2021-10-05 13:10:29 +02:00
block.c migration: using trace_ to replace DPRINTF 2020-10-26 16:15:04 +00:00
block.h migration: disable auto-converge during bulk block migration 2017-09-27 11:27:14 +01:00
channel.c migration: Introduce migration_ioc_[un]register_yank() 2021-07-26 12:44:54 +01:00
channel.h migration: Route errors down through migration_channel_connect 2018-02-06 10:55:12 +00:00
colo-failover.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
colo.c COLO: Move some trace code behind qemu_mutex_unlock_iothread() 2021-12-15 10:31:42 +01:00
dirtyrate.c migration/dirtyrate: implement dirty-bitmap dirtyrate calculation 2021-11-01 22:56:44 +01:00
dirtyrate.h migration/dirtyrate: introduce struct and adjust DirtyRateStat 2021-11-01 22:56:43 +01:00
exec.c migration: unify incoming processing 2018-07-10 12:48:53 +01:00
exec.h migration: Export exec.c functions in its own file 2017-06-01 18:49:22 +02:00
fd.c monitor: Use getter/setter functions for cur_mon 2020-10-09 07:08:19 +02:00
fd.h migration: Fix fd protocol for incoming defer 2019-06-05 12:43:55 +02:00
global_state.c migration: Silence compiler warning in global_state_store_running() 2020-10-02 12:28:48 +01:00
meson.build migration: Move populate_vfio_info() into a separate file 2021-05-14 12:31:51 +02:00
migration.c failover: Silence warning messages during qtest 2021-12-22 08:12:45 +01:00
migration.h migration: provide an error message to migration_cancel() 2021-11-03 09:38:53 +01:00
multifd-zlib.c multifd: Make zlib compression method not use iovs 2021-12-15 10:38:34 +01:00
multifd-zstd.c multifd: Make zstd compression method not use iovs 2021-12-15 10:38:17 +01:00
multifd.c multifd: Shut down the QIO channels to avoid blocking the send threads when they are terminated. 2021-12-15 10:31:42 +01:00
multifd.h multifd: remove used parameter from send_recv_pages() method 2021-12-15 10:31:42 +01:00
page_cache.c migration: Fix cache_init()'s "Failed to allocate" error messages 2021-02-08 11:19:51 +00:00
page_cache.h migration: Clean up signed vs. unsigned XBZRLE cache-size 2021-02-08 11:19:51 +00:00
postcopy-ram.c migration: Check that postcopy fd's are not NULL 2021-11-06 12:35:29 +01:00
postcopy-ram.h migration/: fix some comment spelling errors 2020-09-17 20:36:32 +02:00
qemu-file-channel.c migration: Move the yank unregister of channel_close out 2021-07-26 12:45:03 +01:00
qemu-file-channel.h migration: Export qemu-file-channel.c functions in its own file 2017-05-18 19:20:50 +02:00
qemu-file.c migration: Teach QEMUFile to be QIOChannel-aware 2021-07-26 12:44:59 +01:00
qemu-file.h migration: Teach QEMUFile to be QIOChannel-aware 2021-07-26 12:44:59 +01:00
ram.c migration: Remove is_zero_range() 2021-12-15 10:31:42 +01:00
ram.h Reset the auto-converge counter at every checkpoint. 2021-11-09 08:48:36 +01:00
rdma.c aio-posix: split poll check from ready handler 2022-01-12 17:09:39 +00:00
rdma.h migration: Export rdma.c functions in its own file 2017-06-01 18:49:23 +02:00
savevm.c migration: Never call twice qemu_target_page_size() 2021-12-15 10:31:42 +01:00
savevm.h migration: Add blocker information 2021-02-08 11:19:51 +00:00
socket.c migration/socket: Close the listener at the end 2021-06-08 19:36:19 +01:00
socket.h migration: unify the framework of socket-type channel 2020-08-28 13:34:52 +01:00
target.c migration: Move populate_vfio_info() into a separate file 2021-05-14 12:31:51 +02:00
tls.c migration/tls: Use qcrypto_tls_creds_check_endpoint() 2021-06-29 18:30:20 +01:00
tls.h migration: Fix Lesser GPL version number 2020-11-15 16:43:28 +01:00
trace-events migration/dirtyrate: implement dirty-ring dirtyrate calculation 2021-11-01 22:56:43 +01:00
trace.h trace: switch position of headers to what Meson requires 2020-08-21 06:18:24 -04:00
vmstate-types.c migration: Replace migration's JSON writer by the general one 2020-12-19 10:39:16 +01:00
vmstate.c migration: Replace migration's JSON writer by the general one 2020-12-19 10:39:16 +01:00
xbzrle.c migration: Create migration/xbzrle.h 2017-05-18 18:04:54 +02:00
xbzrle.h migration: Create migration/xbzrle.h 2017-05-18 18:04:54 +02:00
yank_functions.c migration: Move the yank unregister of channel_close out 2021-07-26 12:45:03 +01:00
yank_functions.h migration: Move the yank unregister of channel_close out 2021-07-26 12:45:03 +01:00