[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] TSQ accounting skb->truesize degrades throughput for large packets
On 09/07/2013 12:56 AM, Eric Dumazet wrote: > On Fri, 2013-09-06 at 17:36 +0100, Zoltan Kiss wrote: >> On 06/09/13 13:57, Eric Dumazet wrote: >>> Well, I have no problem to get line rate on 20Gb with a single flow, so >>> other drivers have no problem. >> I've made some tests on bare metal: >> Dell PE R815, Intel 82599EB 10Gb, 3.11-rc4 32 bit kernel with 3.17.3 >> ixgbe (TSO, GSO on), iperf 2.0.5 >> Transmitting packets toward the remote end (so running iperf -c on this >> host) can make 8.3 Gbps with the default 128k tcp_limit_output_bytes. >> When I increased this to 131.506 (128k + 434 bytes) suddenly it jumped >> to 9.4 Gbps. Iperf CPU usage also jumped a few percent from ~36 to ~40% >> (softint percentage in top also increased from ~3 to ~5%) > Typical tradeoff between latency and throughput > > If you favor throughput, then you can increase tcp_limit_output_bytes > > The default is quite reasonable IMHO. > >> So I guess it would be good to revisit the default value of this >> setting. What hw you used Eric for your 20Gb results? > Mellanox CX-3 > > Make sure your NIC doesn't hold TX packets in TX ring too long before > signaling an interrupt for TX completion. Virtio-net orphan the skb in .ndo_start_xmit() so TSQ can not throttle packets in device accurately, and it also can't do BQL. Does this means TSQ should be disabled for virtio-net? _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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