From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [RFC PATCH v8 00/16] Provide a zero-copy method on KVM virtio-net. Date: Sun, 01 Aug 2010 11:18:12 +0300 Message-ID: <4C552DC4.5000600@redhat.com> References: <1280402088-5849-1-git-send-email-xiaohui.xin@intel.com> <1280442682.9058.15.camel@localhost.localdomain> <4C525CD2.5080604@redhat.com> <1280504771.9058.25.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: xiaohui.xin@intel.com, netdev@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mst@redhat.com, mingo@elte.hu, davem@davemloft.net, herbert@gondor.hengli.com.au, jdike@linux.intel.com To: Shirley Ma Return-path: In-Reply-To: <1280504771.9058.25.camel@localhost.localdomain> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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