Re: [Qemu-devel] [PATCH v3 0/7] aio: Support epoll by introducing qemu_poll abstraction

[Stefan Hajnoczi]

On Thu, Apr 16, 2015 at 12:57:29PM +0800, Fam Zheng wrote:
> v3: Rebase to master for 2.4.
>     Although epoll_pwait1 syscall is still being worked on [1], the QEMU part
>     (if any) will base on this, so let's merge it first.
>     
>     That part is not included in this version because I'm still evaluating by
>     comparing epoll_pwait1 with epoll+timerfd as with current master they seem
>     to be really close.
> 
>     [1]: http://www.spinics.net/lists/linux-api/msg08216.html
> 
> 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
> 
> (In high # of fd case, 3 activated but idle virtio-console devices are
> attached, which will add us hundereds of fds to poll)

Have you rerun benchmarks with this patch series?

I wonder how the ppoll-only performance changes.  It seems like there
are now additional copies of <fd, events, revents> information and
corresponding malloc/realloc/frees.

Stefan

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