From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v3 2/2] virtio-ring: Allocate indirect buffers from cache when possible Date: Tue, 04 Sep 2012 19:36:05 +0300 Message-ID: <50462DF5.1000806@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-Transfer-Encoding: 7bit Return-path: In-Reply-To: <50462D8B.7040004@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, Sasha Levin , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On 09/04/2012 07:34 PM, 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? > > Ugh, there's an ugly loop in __find_general_cachep(), which really wants > to be replaced with fls(). > Actually, not, as the loop will be very short for small sizes. -- error compiling committee.c: too many arguments to function