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

aio: Introduce aio-epoll.c

Browse source 
To minimize code duplication, epoll is hooked into aio-posix's
aio_poll() instead of rolling its own. This approach also has both
compile-time and run-time switchability.

1) When QEMU starts with a small number of fds in the event loop, ppoll
is used.

2) When QEMU starts with a big number of fds, or when more devices are
hot plugged, epoll kicks in when the number of fds hits the threshold.

3) Some fds may not support epoll, such as tty based stdio. In this
case, it falls back to ppoll.

A rough benchmark with scsi-disk on virtio-scsi dataplane (epoll gets
enabled from 64 onward). Numbers are in MB/s.

===============================================
             |     master     |     epoll
             |                |
scsi disks # | read    randrw | read    randrw
-------------|----------------|----------------
1            | 86      36     | 92      45
8            | 87      43     | 86      41
64           | 71      32     | 70      38
128          | 48      24     | 58      31
256          | 37      19     | 57      28
===============================================

To comply with aio_{disable,enable}_external, we always use ppoll when
aio_external_disabled() is true.

[Removed #ifdef CONFIG_EPOLL around AioContext epollfd field declaration
since the field is also referenced outside CONFIG_EPOLL code.
--Stefan]

Signed-off-by: Fam Zheng <famz@redhat.com>
Message-id: 1446177989-6702-4-git-send-email-famz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Fam Zheng 2015-10-30 12:06:29 +08:00 • committed by Stefan Hajnoczi
parent 37fcee5d11
commit fbe3fc5cb3
2 changed files with 188 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

5
include/block/aio.h
View file

@ -124,6 +124,11 @@ struct AioContext {
QEMUTimerListGroup tlg;
int external_disable_cnt;
/* epoll(7) state used when built with CONFIG_EPOLL */
int epollfd;
bool epoll_enabled;
bool epoll_available;
};
/**