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Date: Wed, 21 Nov 2012 16:05:27 +0800 From: "Yan, Zheng" <zheng.z.yan@...ux.intel.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: netdev <netdev@...r.kernel.org> Subject: Re: [RFC] tcp: use order-3 pages in tcp_sendmsg() On Thu, Nov 15, 2012 at 9:47 PM, Eric Dumazet <eric.dumazet@...il.com> wrote: > On Thu, 2012-11-15 at 15:52 +0800, Yan, Zheng wrote: >> LLC misses happen on the receiver size. It means most pages allocated by the >> senders are cache hot. But when using order-3 pages, 2048 * 32k = 64M, 64M >> is much larger than LLC size. > > By the way, this 2048*32k is wrong, as the receiver only uses fragments > in pages, and its not related to the "tcp: use order-3 pages in > tcp_sendmsg()" commit > > Many drivers use order-0 pages to hold ethernet frames, regardless of > what was used by the sender ;) > > Hi, I think we found root cause of this regression. The test case runs 2048 instance of netperf TCP loopback stream test on a two sockets core2 machine. There is more LLC misses when using order-3 pages. core2 is not NUMA architecture, there is only one memory node. Order-3 pages used by one socket may be later re-used by another socket, which causes lots of LLC invalidation. Using order-0 page doesn't have this issue is because the kernel page allocator uses per-cpu list to optimize order-0 page allocation. Regards Yan, Zheng -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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