From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shirley Ma Subject: RE: [RFC PATCH 2/2] macvtap: TX zero copy between guest and host kernel Date: Tue, 14 Sep 2010 19:40:52 -0700 Message-ID: <1284518452.13351.111.camel@localhost.localdomain> References: <1284410580.13351.10.camel@localhost.localdomain> <1284410883.13351.14.camel@localhost.localdomain> <20100913.201730.27805132.davem@davemloft.net> <4C8F3C77.7010302@redhat.com> <1284476719.13351.35.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Avi Kivity , David Miller , "arnd@arndb.de" , "mst@redhat.com" , "netdev@vger.kernel.org" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" To: "Xin, Xiaohui" Return-path: Received: from e3.ny.us.ibm.com ([32.97.182.143]:34427 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752244Ab0IOCk6 (ORCPT ); Tue, 14 Sep 2010 22:40:58 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 2010-09-15 at 09:50 +0800, Xin, Xiaohui wrote: > I think what David said is what we have thought before in mp device. > Since we are not sure the exact time the tx buffer was wrote though > DMA operation. > But the deadline is when the tx buffer was freed. So we only notify > the vhost stuff > about the write when tx buffer freed. But the deadline is maybe too > late for performance. Have you tried it? If so what's the performance penalty you have seen by notifying vhost when tx buffer freed? I am thinking to have a callback in skb destructor, vhost_add_used_and_signal gets updated when skb is actually freed, vhost vq & head need to be passed to the callback. This might requires vhost ring size is at least as big as the lower device driver. Thanks Shirley