From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757535Ab2IDSkH (ORCPT ); Tue, 4 Sep 2012 14:40:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:2806 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757504Ab2IDSkF (ORCPT ); Tue, 4 Sep 2012 14:40:05 -0400 Date: Tue, 4 Sep 2012 21:41:22 +0300 From: "Michael S. Tsirkin" To: Avi Kivity Cc: Sasha Levin , rusty@rustcorp.com.au, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v3 2/2] virtio-ring: Allocate indirect buffers from cache when possible Message-ID: <20120904184122.GA3602@redhat.com> References: <1346325718-11151-1-git-send-email-levinsasha928@gmail.com> <1346325718-11151-2-git-send-email-levinsasha928@gmail.com> <20120830133820.GC21132@redhat.com> <50408587.5030603@gmail.com> <20120831095628.GB24244@redhat.com> <50462D8B.7040004@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50462D8B.7040004@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 04, 2012 at 07:34:19PM +0300, Avi Kivity wrote: > On 08/31/2012 12:56 PM, Michael S. Tsirkin wrote: > > On Fri, Aug 31, 2012 at 11:36:07AM +0200, Sasha Levin wrote: > >> On 08/30/2012 03:38 PM, Michael S. Tsirkin wrote: > >> >> +static unsigned int indirect_alloc_thresh = 16; > >> > Why 16? Please make is MAX_SG + 1 this makes some sense. > >> > >> Wouldn't MAX_SG mean we always allocate from the cache? Isn't the memory waste > >> too big in this case? > > > > Sorry. I really meant MAX_SKB_FRAGS + 1. MAX_SKB_FRAGS is 17 so gets us > > threshold of 18. It is less than the size of an skb+shinfo itself so - > > does it look too big to you? Also why do you think 16 is not too big but > > 18 is? If there's a reason then I am fine with 16 too but then please > > put it in code comment near where the value is set. > > > > Yes this means virtio net always allocates from cache > > but this is a good thing, isn't it? Gets us more consistent > > performance. > > kmalloc() also goes to a cache. Is there a measurable difference? Yes see 0/2 and followup discussion. > Ugh, there's an ugly loop in __find_general_cachep(), which really wants > to be replaced with fls(). > > -- > error compiling committee.c: too many arguments to function