From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH 6/6] vhost_net: don't poll on -EFAULT Date: Tue, 17 Apr 2012 07:57:37 +0300 Message-ID: <20120417045736.GA31278@redhat.com> References: <20120416060749.14140.19433.stgit@intel-e5620-16-2.englab.nay.redhat.com> <20120416060833.14140.28139.stgit@intel-e5620-16-2.englab.nay.redhat.com> <20120416071646.GB25396@redhat.com> <4F8BD81A.7010507@redhat.com> <20120416133859.GB13190@redhat.com> <4F8CE305.9090100@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org, xma@us.ibm.com, davem@davemloft.net, linux-kernel@vger.kernel.org, ebiederm@xmission.com To: Jason Wang Return-path: Received: from mx1.redhat.com ([209.132.183.28]:42151 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751148Ab2DQE5a (ORCPT ); Tue, 17 Apr 2012 00:57:30 -0400 Content-Disposition: inline In-Reply-To: <4F8CE305.9090100@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, Apr 17, 2012 at 11:27:01AM +0800, Jason Wang wrote: > On 04/16/2012 09:39 PM, Michael S. Tsirkin wrote: > >On Mon, Apr 16, 2012 at 04:28:10PM +0800, Jason Wang wrote: > >>> On 04/16/2012 03:16 PM, Michael S. Tsirkin wrote: > >>>> >On Mon, Apr 16, 2012 at 02:08:33PM +0800, Jason Wang wrote: > >>>>> >>Currently, we restart tx polling unconditionally when sendmsg() > >>>>> >>fails. This would cause unnecessary wakeups of vhost wokers as it's > >>>>> >>only needed when the socket send buffer were exceeded. > >>>> >Why is this a problem? > >>> > This issue is when guest driver is able to hit the > >>-EFAULT, vhost > >>> discard the the descriptor and restart the polling. This would wake > >>> vhost thread and repeat the loop again which waste cpu. > >Does same thing happen if we get an error from copy from user? > > > > Right, so do you think it makes sense that we only restart polling > on -EAGAIN or -ENOBUFS? Sounds OK. BTW how do you test this? -- MST