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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BE997C433FE for ; Thu, 3 Feb 2022 12:19:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350363AbiBCMTV (ORCPT ); Thu, 3 Feb 2022 07:19:21 -0500 Received: from mail.toke.dk ([45.145.95.12]:41507 "EHLO mail.toke.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235652AbiBCMTU (ORCPT ); Thu, 3 Feb 2022 07:19:20 -0500 From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=toke.dk; s=20161023; t=1643890758; bh=PrA6M+49YlGSC+ysxDmsq2PRS2Pmdw5kBFLOBRlSQB4=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=npQU5Awt+Xbtok5i0OGMi/3RPF3Llp+Z/DD+8V3pD0PB4OODi7uFXdLBMO3c/NAPF GH3fkZ/QflwR/7fjRujd5diT2t8nLLKROyllJN6zfDQ2w7DSNqBhJ0R9LE0tZZ5RFp NeoYAFLvgX/mkmpNDrGqyAj5DTT/DbvqB7e6+2SrXNhn3nQYlHWv+yDHLqstPMrME6 OYddwiJbkEN0uvoBEOF9HEkwKV47gBHo8bAROgcW5+rhu9Jl2oLy3N9f9+nzB0UUcq csCU7avg0SKPUhOoUppzGBs0AgFVopKx203uFkHRLQip3E/1aOE0qR2H4qxMIWpcPy Id4zcs3KTx0nw== To: Eric Dumazet , Sebastian Andrzej Siewior Cc: bpf , netdev , "David S. Miller" , Alexei Starovoitov , Daniel Borkmann , Jakub Kicinski , Jesper Dangaard Brouer , John Fastabend , Thomas Gleixner Subject: Re: [PATCH net-next 3/4] net: dev: Makes sure netif_rx() can be invoked in any context. In-Reply-To: References: <20220202122848.647635-1-bigeasy@linutronix.de> <20220202122848.647635-4-bigeasy@linutronix.de> Date: Thu, 03 Feb 2022 13:19:18 +0100 X-Clacks-Overhead: GNU Terry Pratchett Message-ID: <87o83ob0s9.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Eric Dumazet writes: > On Wed, Feb 2, 2022 at 4:28 AM Sebastian Andrzej Siewior > wrote: >> >> Dave suggested a while ago (eleven years by now) "Let's make netif_rx() >> work in all contexts and get rid of netif_rx_ni()". Eric agreed and >> pointed out that modern devices should use netif_receive_skb() to avoid >> the overhead. >> In the meantime someone added another variant, netif_rx_any_context(), >> which behaves as suggested. >> >> netif_rx() must be invoked with disabled bottom halves to ensure that >> pending softirqs, which were raised within the function, are handled. >> netif_rx_ni() can be invoked only from process context (bottom halves >> must be enabled) because the function handles pending softirqs without >> checking if bottom halves were disabled or not. >> netif_rx_any_context() invokes on the former functions by checking >> in_interrupts(). >> >> netif_rx() could be taught to handle both cases (disabled and enabled >> bottom halves) by simply disabling bottom halves while invoking >> netif_rx_internal(). The local_bh_enable() invocation will then invoke >> pending softirqs only if the BH-disable counter drops to zero. >> >> Add a local_bh_disable() section in netif_rx() to ensure softirqs are >> handled if needed. Make netif_rx_ni() and netif_rx_any_context() invoke >> netif_rx() so they can be removed once they are no more users left. >> >> Link: https://lkml.kernel.org/r/20100415.020246.218622820.davem@davemloft.net >> Signed-off-by: Sebastian Andrzej Siewior > > Maybe worth mentioning this commit will show a negative impact, for > network traffic > over loopback interface. > > My measure of the cost of local_bh_disable()/local_bh_enable() is ~6 > nsec on one of my lab x86 hosts. > > Perhaps we could have a generic netif_rx(), and a __netif_rx() for the > virtual drivers (lo and maybe tunnels). > > void __netif_rx(struct sk_buff *skb); > > static inline int netif_rx(struct sk_buff *skb) > { > int res; > local_bh_disable(); > res = __netif_rx(skb); > local_bh_enable(); > return res; > } +1, this seems like a reasonable solution! -Toke