From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yang Yingliang Subject: Re: [PATCH net v4 1/2] net: sched: tbf: fix calculation of max_size Date: Tue, 3 Dec 2013 19:32:51 +0800 Message-ID: <529DC163.5090403@huawei.com> References: <1386041214-72744-1-git-send-email-yangyingliang@huawei.com> <1386041214-72744-2-git-send-email-yangyingliang@huawei.com> <1386046793.30495.12.camel@edumazet-glaptop2.roam.corp.google.com> <529D8BC7.4050005@huawei.com> <1386058339.30495.19.camel@edumazet-glaptop2.roam.corp.google.com> <529DA8C1.4000504@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: , , , , To: Eric Dumazet Return-path: Received: from szxga02-in.huawei.com ([119.145.14.65]:56547 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752935Ab3LCLd5 (ORCPT ); Tue, 3 Dec 2013 06:33:57 -0500 In-Reply-To: <529DA8C1.4000504@huawei.com> Sender: netdev-owner@vger.kernel.org List-ID: On 2013/12/3 17:47, Yang Yingliang wrote: > On 2013/12/3 16:12, Eric Dumazet wrote: >> On Tue, 2013-12-03 at 15:44 +0800, Yang Yingliang wrote: >>> On 2013/12/3 12:59, Eric Dumazet wrote: >>>> On Tue, 2013-12-03 at 11:26 +0800, Yang Yingliang wrote: >>>> >>>>> + for (max_size = 0; max_size < MAX_PKT_LEN; max_size++) >>>>> + if (psched_l2t_ns(&q->rate, max_size) > q->buffer) >>>>> + break; >>>>> + if (--max_size <= 0) >>>>> + goto unlock_done; >>>>> + >>>> >>>> This seems dubious. With your new code, max_size < 65536 >>>> >>>> Prior code had : >>>> >>>> for (n = 0; n < 256; n++) >>>> if (rtab->data[n] > qopt->buffer) >>>> break; >>>> max_size = (n << qopt->rate.cell_log) - 1; >>>> >>>> So we could have much bigger max_size. >>>> >>>> The reason I ask is that its possible to have qdisc_pkt_len(skb) being >>>> bigger than 65536, for TCP packets with low MSS value. >>>> >>> >>> Hmmm, if qdisc_pkt_len(skb) is bigger than 65536, skb_is_gso(skb) is true, >>> it will go into tbf_segment(). If I am wrong, please point me out, thanks! >>> >>> BTW, 65536 is suggested by Jesper, I'm a little uncertain about it. He is, too. >>> Do you or some other developers have stronger opinions on this? >> >> We do not want to go to tbf_segment() if we programmed tbf to allow TSO >> packets of 68.000 bytes being sent without being segmented. > > I mean a 64KB TSO packet's "qdisc_pkt_len(skb)" is bigger than 65536, but it will go > to tbf_segment(), so the TSO packet of 64KB can be enqueued. I misunderstood 68.000 bytes as 68 bytes, ignore it.:) > >> >> TSO packet of 64KB -> about 45 frames if MSS=1448, 45*1514 = 68130 bytes Maybe MAX_PKT_LEN should be much bigger. Hmm, I'm uncertain how big is the proper value.