Re: [RFC PATCH v8 00/16] Provide a zero-copy method on KVM virtio-net.

[Avi Kivity]

 On 07/30/2010 06:46 PM, Shirley Ma wrote:
> Hello Avi,
>
> On Fri, 2010-07-30 at 08:02 +0300, Avi Kivity wrote:
> > get_user_pages() is indeed slow.  But what about
> > get_user_pages_fast()?
> >
> > Note that when the page is first touched, get_user_pages_fast() falls
> > back to get_user_pages(), so the latency needs to be measured after
> > quite a bit of warm-up.
> Yes, I used get_user_pages_fast, however if falled back to
> get_user_pages() when the apps doesn't allocate buffer on the same page.
> If I run a single ping, the RTT is extremely high, but when running
> multiple pings, the RTT time reduce significantly, but still it is not
> as fast as copy from my initial test. I am thinking that we might need
> to pre-pin memory pool.

I don't understand.  Under what conditions do you use get_user_pages() 
instead of get_user_pages_fast()?  Why?

--
error compiling committee.c: too many arguments to function

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