Re: Benchmarking for vhost polling patch
Hi Michael, Hi Razya, On the netperf benchmark, it looks like polling=10 gives a modest but measureable gain. So from that perspective it might be worth it if it's not too much code, though we'll need to spend more time checking the macro effect - we barely moved the needle on the macro benchmark and that is suspicious. I ran memcached with various values for the key value arguments, and managed to see a bigger impact of polling than when I used the default values, Here are the numbers: key=250 TPS netvhost vm TPS/cpu TPS/CPU value=2048 rate util util change polling=0 101540 103.0 46 100 695.47 polling=5 136747 123.0 83 100 747.25 0.074440609 polling=7 140722 125.7 84 100 764.79 0.099663658 polling=10 141719 126.3 87 100 757.85 0.089688003 polling=15 142430 127.1 90 100 749.63 0.077863015 polling=25 146347 128.7 95 100 750.49 0.079107993 polling=50 150882 131.1 100 100 754.41 0.084733701 Macro benchmarks are less I/O intensive than the micro benchmark, which is why we can expect less impact for polling as compared to netperf. However, as shown above, we managed to get 10% TPS/CPU improvement with the polling patch. Is there a chance you are actually trading latency for throughput? do you observe any effect on latency? No. How about trying some other benchmark, e.g. NFS? Tried, but didn't have enough I/O produced (vhost was at most at 15% util) Also, I am wondering: since vhost thread is polling in kernel anyway, shouldn't we try and poll the host NIC? that would likely reduce at least the latency significantly, won't it? Yes, it could be a great addition at some point, but needs a thorough investigation. In any case, not a part of this patch... Thanks, Razya -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Benchmarking for vhost polling patch
On Sun, Nov 16, 2014 at 02:08:49PM +0200, Razya Ladelsky wrote: Razya Ladelsky/Haifa/IBM@IBMIL wrote on 29/10/2014 02:38:31 PM: From: Razya Ladelsky/Haifa/IBM@IBMIL To: m...@redhat.com Cc: Razya Ladelsky/Haifa/IBM@IBMIL, Alex Glikson/Haifa/IBM@IBMIL, Eran Raichstein/Haifa/IBM@IBMIL, Yossi Kuperman1/Haifa/IBM@IBMIL, Joel Nider/Haifa/IBM@IBMIL, abel.gor...@gmail.com, kvm@vger.kernel.org Date: 29/10/2014 02:38 PM Subject: Benchmarking for vhost polling patch Hi Michael, Following the polling patch thread: http://marc.info/? l=kvmm=140853271510179w=2, I changed poll_stop_idle to be counted in micro seconds, and carried out experiments using varying sizes of this value. If it makes sense to you, I will continue with the other changes requested for the patch. Thank you, Razya Dear Michael, I'm still interested in hearing your opinion about these numbers http://marc.info/?l=kvmm=141458631532669w=2, and whether it is worthwhile to continue with the polling patch. Thank you, Razya Hi Razya, On the netperf benchmark, it looks like polling=10 gives a modest but measureable gain. So from that perspective it might be worth it if it's not too much code, though we'll need to spend more time checking the macro effect - we barely moved the needle on the macro benchmark and that is suspicious. Is there a chance you are actually trading latency for throughput? do you observe any effect on latency? How about trying some other benchmark, e.g. NFS? Also, I am wondering: since vhost thread is polling in kernel anyway, shouldn't we try and poll the host NIC? that would likely reduce at least the latency significantly, won't it? -- MST -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Benchmarking for vhost polling patch
Razya Ladelsky/Haifa/IBM@IBMIL wrote on 29/10/2014 02:38:31 PM: From: Razya Ladelsky/Haifa/IBM@IBMIL To: m...@redhat.com Cc: Razya Ladelsky/Haifa/IBM@IBMIL, Alex Glikson/Haifa/IBM@IBMIL, Eran Raichstein/Haifa/IBM@IBMIL, Yossi Kuperman1/Haifa/IBM@IBMIL, Joel Nider/Haifa/IBM@IBMIL, abel.gor...@gmail.com, kvm@vger.kernel.org Date: 29/10/2014 02:38 PM Subject: Benchmarking for vhost polling patch Hi Michael, Following the polling patch thread: http://marc.info/? l=kvmm=140853271510179w=2, I changed poll_stop_idle to be counted in micro seconds, and carried out experiments using varying sizes of this value. If it makes sense to you, I will continue with the other changes requested for the patch. Thank you, Razya Hi Michael, Have you had the chance to look into these numbers? Thank you, Razya -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Benchmarking for vhost polling patch
Hi Michael, Following the polling patch thread: http://marc.info/?l=kvmm=140853271510179w=2, I changed poll_stop_idle to be counted in micro seconds, and carried out experiments using varying sizes of this value. The setup for netperf consisted of 1 vm and 1 vhost , each running on their own dedicated core. Could you provide your changing code? Thanks, Zhang Haoyu -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Benchmarking for vhost polling patch
Zhang Haoyu zhan...@sangfor.com wrote on 30/10/2014 01:30:08 PM: From: Zhang Haoyu zhan...@sangfor.com To: Razya Ladelsky/Haifa/IBM@IBMIL, mst m...@redhat.com Cc: Razya Ladelsky/Haifa/IBM@IBMIL, kvm kvm@vger.kernel.org Date: 30/10/2014 01:30 PM Subject: Re: Benchmarking for vhost polling patch Hi Michael, Following the polling patch thread: http://marc.info/? l=kvmm=140853271510179w=2, I changed poll_stop_idle to be counted in micro seconds, and carried out experiments using varying sizes of this value. The setup for netperf consisted of 1 vm and 1 vhost , each running on their own dedicated core. Could you provide your changing code? Thanks, Zhang Haoyu Hi Zhang, Do you mean the change in code for poll_stop_idle? Thanks, Razya -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Benchmarking for vhost polling patch
Hi Michael, Following the polling patch thread: http://marc.info/? l=kvmm=140853271510179w=2, I changed poll_stop_idle to be counted in micro seconds, and carried out experiments using varying sizes of this value. The setup for netperf consisted of 1 vm and 1 vhost , each running on their own dedicated core. Could you provide your changing code? Thanks, Zhang Haoyu Hi Zhang, Do you mean the change in code for poll_stop_idle? Yes, it's better to provide the complete code, including the polling patch. Thanks, Zhang Haoyu Thanks, Razya -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
