From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sasha Levin Subject: Re: [PATCH] kvm tools: Add MMIO coalescing support Date: Sat, 04 Jun 2011 13:14:01 +0300 Message-ID: <1307182441.7239.2.camel@lappy> References: <1307130668-5652-1-git-send-email-levinsasha928@gmail.com> <20110604093847.GB14524@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: penberg@kernel.org, kvm@vger.kernel.org, asias.hejun@gmail.com, gorcunov@gmail.com, prasadjoshi124@gmail.com To: Ingo Molnar Return-path: Received: from mail-wy0-f174.google.com ([74.125.82.174]:52160 "EHLO mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753908Ab1FDKOH (ORCPT ); Sat, 4 Jun 2011 06:14:07 -0400 Received: by wya21 with SMTP id 21so1873722wya.19 for ; Sat, 04 Jun 2011 03:14:06 -0700 (PDT) In-Reply-To: <20110604093847.GB14524@elte.hu> Sender: kvm-owner@vger.kernel.org List-ID: On Sat, 2011-06-04 at 11:38 +0200, Ingo Molnar wrote: > * Sasha Levin wrote: > > > Coalescing MMIO allows us to avoid an exit every time we have a > > MMIO write, instead - MMIO writes are coalesced in a ring which > > can be flushed once an exit for a different reason is needed. > > A MMIO exit is also trigged once the ring is full. > > > > Coalesce all MMIO regions registered in the MMIO mapper. > > Add a coalescing handler under kvm_cpu. > > Does this have any effect on latency? I.e. does the guest side > guarantee that the pending queue will be flushed after a group of > updates have been done? Theres nothing that detects groups of MMIO writes, but the ring size is a bit less than PAGE_SIZE (half of it is overhead - rest is data) and we'll exit once the ring is full. -- Sasha.