Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753850Ab2JVM6d (ORCPT ); Mon, 22 Oct 2012 08:58:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50430 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751125Ab2JVM6c (ORCPT ); Mon, 22 Oct 2012 08:58:32 -0400 Message-ID: <508542EF.5050401@redhat.com> Date: Mon, 22 Oct 2012 14:58:23 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120911 Thunderbird/15.0.1 MIME-Version: 1.0 To: Jan Kiszka CC: Gleb Natapov , Xiao Guangrong , Marcelo Tosatti , LKML , KVM Subject: Re: [PATCH] KVM: x86: fix vcpu->mmio_fragments overflow References: <5081033C.4060503@linux.vnet.ibm.com> <20121022091615.GG29310@redhat.com> <50852972.305@linux.vnet.ibm.com> <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> In-Reply-To: <50854232.8090309@siemens.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1148 Lines: 23 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. -- error compiling committee.c: too many arguments to function -- 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/