From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Chris Friesen" Subject: Re: questions on NAPI processing latency and dropped network packets Date: Mon, 14 Jan 2008 13:25:22 -0600 Message-ID: <478BB722.1020004@nortel.com> References: <478654C3.60806@nortel.com> <2c0942db0801112137k3f3f885ek212d5cbaecb7fea0@mail.gmail.com> <478B8473.6080506@nortel.com> <478B943C.7080009@cosmosbay.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Ray Lee , netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Eric Dumazet Return-path: Received: from zcars04f.nortel.com ([47.129.242.57]:47190 "EHLO zcars04f.nortel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751390AbYANT0O (ORCPT ); Mon, 14 Jan 2008 14:26:14 -0500 In-Reply-To: <478B943C.7080009@cosmosbay.com> Sender: netdev-owner@vger.kernel.org List-ID: Eric Dumazet wrote: > Chris Friesen a =C3=A9crit : >> Based on profiling and instrumentation it seems like the cost of=20 >> sctp_endpoint_lookup_assoc() more than triples, which means that the= =20 >> amount of time that bottom halves are disabled in that function also= =20 >> triples. >=20 > Any idea of the size of sctp hash size you have ? > (your dmesg probably includes a message starting with SCTP: Hash tabl= es=20 > configured... > How many concurrent sctp sockets are handled ? Our lab is currently rebooting, but I'll try and get this once it's bac= k up. > Maybe sctp_assoc_hashfn() is too weak for your use, and some chains a= re=20 > *really* long. Based on the profiling information we're spending time in=20 sctp_endpoint_lookup_assoc() which doesn't actually use hashes, so I=20 can't see how the hash would be related. I'm pretty new to SCTP though= ,=20 so I may be missing something. Here's the top results from readprofile, unfortunately these are=20 aggregated across both cpus so they don't really show what's going on.=20 The key thing is that sctp_endpoint_lookup_assoc() is the most expensiv= e=20 kernel routine on this entire system. 3147 .power4_idle 22.4786 1712 .native_idle 20.3810 1234 .sctp_endpoint_lookup_assoc 2.1725 1212 ._spin_unlock_irqrestore 6.4468 778 .do_futex 0.3791 447 ._spin_unlock_irq 4.2981 313 .fget 1.7784 277 .fput 3.8472 275 .kfree 0.7473 234 .__kmalloc 0.5571 131 SystemCall_common 0.3411 130 .sctp_assoc_is_match 0.6373 123 .lock_sock 0.4155 119 .find_vma 0.6919 116 .kmem_cache_alloc 0.3580 111 .kmem_cache_free 0.3343 106 .skb_release_data 0.4907 102 .__copy_tofrom_user 0.0724 100 .exit_elf_binfmt 1.9231 100 .do_select 0.0820 Chris