Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754053Ab2JVNIS (ORCPT ); Mon, 22 Oct 2012 09:08:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51459 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753279Ab2JVNIR (ORCPT ); Mon, 22 Oct 2012 09:08:17 -0400 Date: Mon, 22 Oct 2012 15:08:10 +0200 From: Gleb Natapov To: Jan Kiszka Cc: Avi Kivity , Xiao Guangrong , Marcelo Tosatti , LKML , KVM Subject: Re: [PATCH] KVM: x86: fix vcpu->mmio_fragments overflow Message-ID: <20121022130810.GW29310@redhat.com> References: <20121022112314.GO29310@redhat.com> <50852F9C.9020808@siemens.com> <20121022114311.GQ29310@redhat.com> <508531E1.2030307@siemens.com> <508539A8.40404@redhat.com> <50853FF1.8010809@siemens.com> <20121022125301.GS29310@redhat.com> <50854232.8090309@siemens.com> <508542EF.5050401@redhat.com> <508544B6.6070301@siemens.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <508544B6.6070301@siemens.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1439 Lines: 30 On Mon, Oct 22, 2012 at 03:05:58PM +0200, Jan Kiszka wrote: > On 2012-10-22 14:58, Avi Kivity wrote: > > On 10/22/2012 02:55 PM, Jan Kiszka wrote: > >>> Since the userspace change is needed the idea is dead, but if we could > >>> implement it I do not see how it can hurt the latency if it would be the > >>> only mechanism to use coalesced mmio buffer. Checking that the ring buffer > >>> is empty is cheap and if it is not empty it means that kernel just saved > >>> you a lot of 8 bytes exists so even after iterating over all the entries there > >>> you still saved a lot of time. > >> > >> When taking an exit for A, I'm not interesting in flushing stuff for B > >> unless I have a dependency. Thus, buffers would have to be per device > >> before extending their use. > > > > Any mmio exit has to flush everything. For example a DMA caused by an > > e1000 write has to see any writes to the framebuffer, in case the guest > > is transmitting its framebuffer to the outside world. > > We already flush when that crazy guest actually accesses the region, no > need to do this unconditionally. > What if framebuffer is accessed from inside the kernel? Is this case handled? -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/