Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755817Ab3GYLBs (ORCPT ); Thu, 25 Jul 2013 07:01:48 -0400 Received: from mail-vb0-f47.google.com ([209.85.212.47]:53044 "EHLO mail-vb0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755591Ab3GYLBp (ORCPT ); Thu, 25 Jul 2013 07:01:45 -0400 Message-ID: <1374750101.23313.16.camel@edumazet-glaptop> Subject: Re: [PATCH 1/1] TX throttling bug-fixing patch of AX88179_178A From: Eric Dumazet To: Ming Lei Cc: Ben Hutchings , Oliver Neukum , Grant Grundler , Freddy Xin , David Miller , netdev , linux-usb@vger.kernel.org, LKML , ASIX Louis =?UTF-8?Q?=5B=E8=98=87=E5=A8=81=E9=99=B8=5D?= , Allan Chou Date: Thu, 25 Jul 2013 04:01:41 -0700 In-Reply-To: References: <1374311809-4155-1-git-send-email-freddy@asix.com.tw> <1374512879.4990.19.camel@edumazet-glaptop> <1374518312.1635.29.camel@bwh-desktop.uk.level5networks.com> <1374518841.4990.26.camel@edumazet-glaptop> <1374522471.1635.48.camel@bwh-desktop.uk.level5networks.com> <1374559827.4990.143.camel@edumazet-glaptop> <1374729058.23313.8.camel@edumazet-glaptop> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1696 Lines: 40 On Thu, 2013-07-25 at 13:25 +0800, Ming Lei wrote: > On Thu, Jul 25, 2013 at 1:10 PM, Eric Dumazet wrote: > > On Thu, 2013-07-25 at 10:28 +0800, Ming Lei wrote: > > > >> > >> It depends if size of sg buffer(except for last one) in the sg list can be > >> divided by usb endpoint's max packet size(512 or 1024), at least there > >> is the constraint: > >> > >> http://git.kernel.org/cgit/linux/kernel/git/gregkh/usb.git/commit/?h=usb-next&id=10e232c597ac757e7f8600649f7e872e86de190f > >> > >> I am wondering if network stack can meet that. If not, it might be a > >> bit difficult > >> because lots of USB host controller don't support that, and driver may have > >> to support SG and non-SG at the same time for working well on all HCs. > > > > I do not see the problem. > > > > If one skb has 2 fragments of 32KB, couldn't they be split into 64 1K > > segments by the device driver ? > > OK, if length of fragments of all SKBs from network stack can always guarantee > to be divided by 1024, that is fine, seems I worry about too much, :-) Unfortunately, there is no such guarantee. TSO permits sendfile() zero copy operation, so the frags can be of any size, any offset... In this mode, the first element (skb->head) will typically contains the headers, and there are way below 512 bytes. So even with lowering netdev->gso_max_size under PAGE_SIZE, most of the packets will need to be copied into a single segment. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/