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Re: [Qemu-devel] [RFC 0/3] aio: experimental virtio-blk polling mode
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [RFC 0/3] aio: experimental virtio-blk polling mode |
Date: |
Tue, 15 Nov 2016 01:13:14 +0800 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
On Mon, 11/14 17:06, Stefan Hajnoczi wrote:
> On Mon, Nov 14, 2016 at 04:29:49PM +0100, Paolo Bonzini wrote:
> > On 14/11/2016 16:26, Stefan Hajnoczi wrote:
> > > On Fri, Nov 11, 2016 at 01:59:25PM -0600, Karl Rister wrote:
> > >> QEMU_AIO_POLL_MAX_NS IOPs
> > >> unset 31,383
> > >> 1 46,860
> > >> 2 46,440
> > >> 4 35,246
> > >> 8 34,973
> > >> 16 46,794
> > >> 32 46,729
> > >> 64 35,520
> > >> 128 45,902
> > >
> > > The environment variable is in nanoseconds. The range of values you
> > > tried are very small (all <1 usec). It would be interesting to try
> > > larger values in the ballpark of the latencies you have traced. For
> > > example 2000, 4000, 8000, 16000, and 32000 ns.
> > >
> > > Very interesting that QEMU_AIO_POLL_MAX_NS=1 performs so well without
> > > much CPU overhead.
> >
> > That basically means "avoid a syscall if you already know there's
> > something to do", so in retrospect it's not that surprising. Still
> > interesting though, and it means that the feature is useful even if you
> > don't have CPU to waste.
>
> Can you spell out which syscall you mean? Reading the ioeventfd?
>
> The benchmark uses virtio-blk dataplane and iodepth=1 so there shouldn't
> be much IOThread event loop activity besides the single I/O request.
>
> The reason this puzzles me is that I wouldn't expect poll to succeed
> with QEMU_AIO_POLL_MAX_NS and iodepth=1.
I see the guest shouldn't send more requests, but isn't it possible for
the linux-aio poll to succeed?
Fam
>
> Thanks,
> Stefan
- Re: [Qemu-devel] [RFC 1/3] aio-posix: add aio_set_poll_handler(), (continued)
- Re: [Qemu-devel] [RFC 0/3] aio: experimental virtio-blk polling mode, Fam Zheng, 2016/11/16
- Re: [Qemu-devel] [RFC 0/3] aio: experimental virtio-blk polling mode, Karl Rister, 2016/11/14
- Re: [Qemu-devel] [RFC 0/3] aio: experimental virtio-blk polling mode, Karl Rister, 2016/11/14
- Re: [Qemu-devel] [RFC 0/3] aio: experimental virtio-blk polling mode, Paolo Bonzini, 2016/11/14
- Re: [Qemu-devel] [RFC 0/3] aio: experimental virtio-blk polling mode, Stefan Hajnoczi, 2016/11/15
- Re: [Qemu-devel] [RFC 0/3] aio: experimental virtio-blk polling mode, Karl Rister, 2016/11/15
Re: [Qemu-devel] [RFC 0/3] aio: experimental virtio-blk polling mode, no-reply, 2016/11/13
Re: [Qemu-devel] [RFC 0/3] aio: experimental virtio-blk polling mode, Christian Borntraeger, 2016/11/14