From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [v2 RFC PATCH 0/4] Implement multiqueue virtio-net Date: Sun, 19 Sep 2010 14:44:43 +0200 Message-ID: <20100919124443.GJ7350@redhat.com> References: <20100917100307.21276.79185.sendpatchset@krkumar2.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: rusty@rustcorp.com.au, davem@davemloft.net, kvm@vger.kernel.org, arnd@arndb.de, netdev@vger.kernel.org, avi@redhat.com, anthony@codemonkey.ws To: Krishna Kumar Return-path: Content-Disposition: inline In-Reply-To: <20100917100307.21276.79185.sendpatchset@krkumar2.in.ibm.com> Sender: kvm-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, Sep 17, 2010 at 03:33:07PM +0530, Krishna Kumar wrote: > For 1 TCP netperf, I ran 7 iterations and summed it. Explanation > for degradation for 1 stream case: Could you document how exactly do you measure multistream bandwidth: netperf flags, etc? > 1. Without any tuning, BW falls -6.5%. Any idea where does this come from? Do you see more TX interrupts? RX interrupts? Exits? Do interrupts bounce more between guest CPUs? > 2. When vhosts on server were bound to CPU0, BW was as good > as with original code. > 3. When new code was started with numtxqs=1 (or mq=off, which > is the default), there was no degradation. > > Next steps: > ----------- > 1. MQ RX patch is also complete - plan to submit once TX is OK (as > well as after identifying bandwidth degradations for some test > cases). > 2. Cache-align data structures: I didn't see any BW/SD improvement > after making the sq's (and similarly for vhost) cache-aligned > statically: > struct virtnet_info { > ... > struct send_queue sq[16] ____cacheline_aligned_in_smp; > ... > }; > 3. Migration is not tested. 4. Identify reasons for single netperf BW regression. 5. Test perf in more scenarious: small packets host -> guest guest <-> external in last case: find some other way to measure host CPU utilization, try multiqueue and single queue devices 6. Use above to figure out what is a sane default for numtxqs. > > Review/feedback appreciated. > > Signed-off-by: Krishna Kumar > ---