From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-17.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EB778C433DF for ; Thu, 27 Aug 2020 11:49:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C51F622BF3 for ; Thu, 27 Aug 2020 11:49:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="U/C0BJII" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728915AbgH0Ls4 (ORCPT ); Thu, 27 Aug 2020 07:48:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59000 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728742AbgH0Lfu (ORCPT ); Thu, 27 Aug 2020 07:35:50 -0400 Received: from mail-il1-x143.google.com (mail-il1-x143.google.com [IPv6:2607:f8b0:4864:20::143]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4FA09C06121B for ; Thu, 27 Aug 2020 04:35:45 -0700 (PDT) Received: by mail-il1-x143.google.com with SMTP id q14so4579296ilm.2 for ; Thu, 27 Aug 2020 04:35:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=nk3XMsscwoEZw1pfmEYAb8eP1m4cERKtDNn3BOQ6wZo=; b=U/C0BJIItk4cpBQIKKHprsucVwFzLLWgqyxYVTuviqiRvJjFV00mPKgYgU/U7w4t9Q Y40T9K2BvdJWBQDj0tw6ewwLwDyW1ggK0A40/SxM6ZC0MKMxWAcf8PU1zP7NJ0DL7mwD mabdMS5DBW7DARO/TJRFwzlgPVu8S0VESQgV96hED2alyqd76GfOWzrgDjc3gWEb5N5f ZXoX2eU3bk3e00NNtglqOZOkh7D0oiLs7icsqPvxkUgCc0SrWpmEME3fJ2zGpsL7xeGb Os6qqgp8yE/vPgMSIJW3N5qhxl98XatED8SwbtCvliPqsXhjaCEIi87d3MLFeclXamQ9 +NzA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=nk3XMsscwoEZw1pfmEYAb8eP1m4cERKtDNn3BOQ6wZo=; b=aDsLs3zq3KGllS+Urj3pEAQzcdfcDe6J5yVt6F3Fdz+DNa6jXJrNF4X3XpWQzs/9zv aF0g8E247NKcuOC6ahBloYhpNAisL3OkOeJDVDo/fZEIgwYq9BXJ7W4d5xHLWlUGxjvF dnqmTyIOmycj/fHXz8T918dJo3pttfwR3o3I1kjq5y2TFeb/hcJczM4Dw8aTb/dPnTo3 ZhyEmNNmXSwnsj0YvrNkZzxcnP9sE93tgRx533KVm2LDfrVeiXrWSDLQu6LO1n7Yrooq 8xdt5ZC71bFRV01XZS6KlOf8NoZ0/i06mPWOlqG3CqRV8QQ2jB6pTqFVUUSzXVU9GAtn zOSA== X-Gm-Message-State: AOAM530+KC6p6LFKd5X6CH/JMsuQe6Ujig8drnbtUuNSvepAxgS9jMxt h+vK7p1BOmt30gMi3Ok0jYVmCuMPghosFs2ShQwNHw== X-Google-Smtp-Source: ABdhPJwxSXQ2/aSL9AbPqwXrgVZPAyH+csHxjYXsclhJT00Mv6s7Ff00Pw0g3zQXn7UCx/ACkT8asEAMiK59f/Wo/HY= X-Received: by 2002:a92:bb0e:: with SMTP id w14mr15038915ili.68.1598528144077; Thu, 27 Aug 2020 04:35:44 -0700 (PDT) MIME-Version: 1.0 References: <20200827112922.48889-1-linmiaohe@huawei.com> In-Reply-To: <20200827112922.48889-1-linmiaohe@huawei.com> From: Eric Dumazet Date: Thu, 27 Aug 2020 04:35:32 -0700 Message-ID: Subject: Re: [PATCH] net: Set trailer iff skb1 is the last one To: Miaohe Lin Cc: David Miller , Jakub Kicinski , Pravin B Shelar , Florian Westphal , martin.varghese@nokia.com, Davide Caratti , Steffen Klassert , Paolo Abeni , shmulik@metanetworks.com, kyk.segfault@gmail.com, netdev , LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 27, 2020 at 4:31 AM Miaohe Lin wrote: > > Set trailer iff skb1 is the skbuff where the tailbits space begins. > > Signed-off-by: Miaohe Lin > --- > net/core/skbuff.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index 0b24aed04060..18ed56316e56 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -4488,8 +4488,9 @@ int skb_cow_data(struct sk_buff *skb, int tailbits, struct sk_buff **trailer) > skb1 = skb2; > } > elt++; > - *trailer = skb1; > skb_p = &skb1->next; > + if (!*skb_p) > + *trailer = skb1; > Why is adding a conditional test going to help ? cpu will have hard time predicting this one, I doubt this kind of change is a win.