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Date: Tue, 10 May 2016 14:30:17 +0200 From: Jesper Dangaard Brouer <brouer@...hat.com> To: Alexander Duyck <alexander.duyck@...il.com> Cc: Netdev <netdev@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>, Saeed Mahameed <saeedm@...lanox.com>, Or Gerlitz <gerlitz.or@...il.com>, Eugenia Emantayev <eugenia@...lanox.com>, brouer@...hat.com Subject: Re: [net-next PATCH V1 1/3] net: bulk alloc and reuse of SKBs in NAPI context On Mon, 9 May 2016 13:46:32 -0700 Alexander Duyck <alexander.duyck@...il.com> wrote: > Try testing with TCP_RR instead and watch the CPU utilization. I'm > suspecting allocating 8 and freeing 7 buffers for every 1 buffer > received will blow any gains right out of the water. Also try it with > a mix of traffic. So have one NIC doing TCP_RR while another is doing > a stream test. You are stuffing 7 buffers onto a queue that were were > using to perform bulk freeing. How much of a penalty do you take if > you are now limited on how many you can bulk free because somebody > left a stray 7 packets sitting on the queue? Testing with TCP_RR, is not a very "clean" network test. One have to be very careful what is actually being tested, is it the server or client which is the bottleneck. And most of all this is test of the CPU/process scheduler. We can avoid the scheduler problem by enabling busy_poll/busy_read. I guess you want to see the "scheduler test" first. Default setting of disabled busy poll on both client and server: Disable busy poll on both client and server, Not patched: $ netperf -H 198.18.40.2 -t TCP_RR -l 60 -T 6,6 -Cc MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 198.18.40.2 () port 0 AF_INET : histogram : demo : first burst 0 : cpu bind Local /Remote Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem Send Recv Size Size Time Rate local remote local remote bytes bytes bytes bytes secs. per sec % S % S us/Tr us/Tr 16384 87380 1 1 60.00 78077.55 3.74 2.69 3.830 8.265 16384 87380 Disable busy poll on both client and server, patched: $ netperf -H 198.18.40.2 -t TCP_RR -l 60 -T 6,6 -Cc MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 198.18.40.2 () port 0 AF_INET : histogram : demo : first burst 0 : cpu bind Local /Remote Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem Send Recv Size Size Time Rate local remote local remote bytes bytes bytes bytes secs. per sec % S % S us/Tr us/Tr 16384 87380 1 1 60.00 78517.32 3.06 2.84 3.118 8.677 16384 87380 I will not call this an improvement... the results are basically the same. Next step enabling busy poll on the server. The server is likely the bottleneck, given it's CPU is slower than the client. Context switches on the server is too high 156K/sec, after enabling busy poll reduced to 620/sec. Note the client is doing around 233k/sec context switches, (fairly impressive). Enabling busy poll on the server: sysctl -w net.core.busy_poll=50 sysctl -w net.core.busy_read=50 Enabled busy poll only on server, Not patched: $ netperf -H 198.18.40.2 -t TCP_RR -l 60 -T 6,6 -Cc MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 198.18.40.2 () port 0 AF_INET : histogram : demo : first burst 0 : cpu bind Local /Remote Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem Send Recv Size Size Time Rate local remote local remote bytes bytes bytes bytes secs. per sec % S % S us/Tr us/Tr 16384 87380 1 1 60.00 112480.72 5.90 4.68 4.194 9.984 16384 87380 Enabled busy poll only on server, patched: $ netperf -H 198.18.40.2 -t TCP_RR -l 60 -T 6,6 -Cc MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 198.18.40.2 () port 0 AF_INET : histogram : demo : first burst 0 : cpu bind Local /Remote Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem Send Recv Size Size Time Rate local remote local remote bytes bytes bytes bytes secs. per sec % S % S us/Tr us/Tr 16384 87380 1 1 60.00 110152.34 5.84 4.60 4.242 10.014 16384 87380 Numbers are too close, for any conclusions. Running a second run, on Not-patched kernel: Enabled busy poll only on server, Not patched: [jbrouer@...yon ~]$ netperf -H 198.18.40.2 -t TCP_RR -l 60 -T 6,6 -Cc MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 198.18.40.2 () port 0 AF_INET : histogram : demo : first burst 0 : cpu bind Local /Remote Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem Send Recv Size Size Time Rate local remote local remote bytes bytes bytes bytes secs. per sec % S % S us/Tr us/Tr 16384 87380 1 1 60.00 101554.90 4.12 4.31 3.245 10.185 16384 87380 Thus, variation between runs are bigger than any improvement/regression, thus no performance conclusions from this change can be drawn. Lets move beyond testing the CPU/process scheduler by enabling busy-polling on both client and server: (sysctl -w net.core.busy_poll=50 ;sysctl -w net.core.busy_read=50) Enable busy poll on both client and server, Not patched: $ netperf -H 198.18.40.2 -t TCP_RR -l 60 -T 6,6 -Cc MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 198.18.40.2 () port 0 AF_INET : histogram : demo : first burst 0 : cpu bind Local /Remote Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem Send Recv Size Size Time Rate local remote local remote bytes bytes bytes bytes secs. per sec % S % S us/Tr us/Tr 16384 87380 1 1 60.00 137987.86 13.18 4.77 7.643 8.298 16384 87380 Enable busy poll on both client and server, patched: $ netperf -H 198.18.40.2 -t TCP_RR -l 60 -T 6,6 -Cc MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 198.18.40.2 () port 0 AF_INET : histogram : demo : first burst 0 : cpu bind Local /Remote Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem Send Recv Size Size Time Rate local remote local remote bytes bytes bytes bytes secs. per sec % S % S us/Tr us/Tr 16384 87380 1 1 60.00 147324.38 13.76 4.76 7.474 7.747 16384 87380 I've a little bit surprised to see such a large improvement here 6.76%. 147324/137987*100 = 106.76 I'm remaining skeptic towards this measurement, as the improvement should not be this high. Even if recycling is happening. Perf record does show less calls to __slab_free(), indicating better interaction with SLUB, and perhaps recycling working. But this is only a perf-report change from 0.37% to 0.33%. More testing show not-patched kernel fluctuate between 125k-143k/sec, and patched kernel fluctuate between 131k-152k/sec. The ranges are too high, to say anything conclusive. It seems to be timing dependent, as starting and stoping the test with -D 1, show a rate variation within 2k/sec, but rate itself can vary withing the range stated. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer
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