From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH] fix reading from character devices Date: Mon, 21 Jan 2008 12:50:14 +0200 Message-ID: <479478E6.6030903@qumranet.com> References: <47946610.9040001@siemens.com> <47947045.6040106@qumranet.com> <1200912198.3188.6.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, Jan Kiszka To: dor.laor-atKUWr5tajBWk0Htik3J/w@public.gmane.org Return-path: In-Reply-To: <1200912198.3188.6.camel-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Dor Laor wrote: > On Mon, 2008-01-21 at 12:13 +0200, Avi Kivity wrote: > >> Jan Kiszka wrote: >> >>> Hi Avi, >>> >>> commit "kvm: qemu: consume all pending I/O in I/O loop" >>> (8ab8bb09f1115b9bf733f885cc92b6c63d83f420) broke reading data bursts >>> from serial devices (and maybe from other character devices as well) by >>> guests. Reason: serial devices do input flow control via fd_read_poll, >>> but qemu now ignores this fact by pushing all data into the virtual >>> device as soon as it is available. >>> >>> Patch below is not really nice (just as the whole internal virtual I/O >>> interface at the moment, IMHO), but it re-enables the serial ports for >>> now. >>> >>> >>> >> I'm worried that it will break Dor's hack that speeds up virtio. Dor? >> >> > > It should be fine. Tap device without my hack has fd_read_poll null and > I hacked it to have a handler that returns false if virtio is used and > true otherwise. > So Jan's patch should set 'more' to 1 and it will be like before. > > But if virtio is used with this patch, it won't set 'more' to 1. Will virtio handle it or will throughput drop to be related to whatever timers we have set up? -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/