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

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 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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