[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH v2 0/6] aio: Support epoll by introducing qemu_p
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH v2 0/6] aio: Support epoll by introducing qemu_poll abstraction |
Date: |
Tue, 16 Dec 2014 10:04:38 +0800 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Thu, 12/04 11:43, Fam Zheng wrote:
> v2: Emulate nanoseconds precison of timeout with ppoll and timerfd.
> Their performance is on par with each other, but both much better than
> qemu.git:
>
> syscall high # of fd low # of fd
> -------------------------------------------------
> qemu.git(ppoll) 44 96
> ppoll+epoll 85 101
> timerfd+epoll 87 109
More data points.
Xiaomei tested this series (applied on top of RHEL 7 qemu-kvm-rhev) and found
that:
0) when # of fds is high, epoll solutions are much better (+30%).
1) timerfd+epoll is slightly better than ppoll+epoll, but the difference is
minimal.
2) original code is 2%~5% faster than the new implementations when # of fds is
low.
This leads to the conclusion that that we'll have a small performance
degradation if merge this series. I'm thinking about possible optimizations.
Options in my mind are:
1) Remove 1ns PR_SET_TIMERSLACK in timerfd+epoll, this doesn't make qemu_poll
faster than the old qemu_poll_ns, but may have other positive effects that
compensate the cost.
2) Use dynamic switch between ppoll and timerfd+epoll. In poll-linux.c, We
start with pure ppoll, while keeping track of elapsed time in ppoll. And
periodically, we try "timerfd+epoll" for a few iterations, so that we can
compare if it is faster than pure ppoll. If it is, swap them, use timerfd+epoll
and and periodically try "ppoll".
That said, I'll also look at the kernel side. Maybe optimizing ppoll or just
add EPOLL_NANOSECOND_TIMEOUT to epoll_create1 is a better place for
engineering.
Fam
>
> (In high # of fd case, 3 activated but idle virtio-console devices are
> attached, which will add us hundereds of fds to poll)
>
> v1 cover letter
> ---------------
>
> ppoll(2) doesn't scale as well as epoll: The elapsed time of the syscall is
> linear to the number of fd's we poll, which hurts performance a bit when the
> number of devices are many, or when a virtio device registers many virtqueues
> (virtio-serial, for instance).
>
> This series introduces qemu_poll, which is implemented with g_poll and epoll,
> decided at configure time with CONFIG_EPOLL.
>
> Fam
>
>
> Fam Zheng (6):
> poll: Introduce QEMU Poll API
> posix-aio: Use QEMU poll interface
> poll: Add epoll implementation for qemu_poll
> main-loop: Replace qemu_poll_ns with qemu_poll
> tests: Add test case for qemu_poll
> poll-linux: Add timerfd support
>
> Makefile.objs | 2 +
> aio-posix.c | 52 ++++----
> async.c | 5 +-
> include/block/aio.h | 7 +-
> include/qemu/poll.h | 40 ++++++
> include/qemu/timer.h | 13 --
> include/qemu/typedefs.h | 2 +
> main-loop.c | 35 +++++-
> poll-glib.c | 130 ++++++++++++++++++++
> poll-linux.c | 314
> ++++++++++++++++++++++++++++++++++++++++++++++++
> qemu-timer.c | 28 -----
> tests/Makefile | 2 +
> tests/test-poll.c | 272 +++++++++++++++++++++++++++++++++++++++++
> 13 files changed, 821 insertions(+), 81 deletions(-)
> create mode 100644 include/qemu/poll.h
> create mode 100644 poll-glib.c
> create mode 100644 poll-linux.c
> create mode 100644 tests/test-poll.c
>
> --
> 1.9.3
>
>
- [Qemu-devel] [PATCH v2 0/6] aio: Support epoll by introducing qemu_poll abstraction, Fam Zheng, 2014/12/03
- [Qemu-devel] [PATCH v2 1/6] poll: Introduce QEMU Poll API, Fam Zheng, 2014/12/03
- [Qemu-devel] [PATCH v2 2/6] posix-aio: Use QEMU poll interface, Fam Zheng, 2014/12/03
- [Qemu-devel] [PATCH v2 3/6] poll: Add epoll implementation for qemu_poll, Fam Zheng, 2014/12/03
- [Qemu-devel] [PATCH v2 4/6] main-loop: Replace qemu_poll_ns with qemu_poll, Fam Zheng, 2014/12/03
- [Qemu-devel] [PATCH v2 5/6] tests: Add test case for qemu_poll, Fam Zheng, 2014/12/03
- [Qemu-devel] [PATCH v2 6/6] poll-linux: Add timerfd support, Fam Zheng, 2014/12/03
- Re: [Qemu-devel] [PATCH v2 0/6] aio: Support epoll by introducing qemu_poll abstraction,
Fam Zheng <=