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=-8.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 BC0ADC4727F for ; Thu, 24 Sep 2020 22:03:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7084723AA3 for ; Thu, 24 Sep 2020 22:03:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726638AbgIXWDT (ORCPT ); Thu, 24 Sep 2020 18:03:19 -0400 Received: from www62.your-server.de ([213.133.104.62]:48674 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726205AbgIXWDS (ORCPT ); Thu, 24 Sep 2020 18:03:18 -0400 Received: from sslproxy01.your-server.de ([78.46.139.224]) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89_1) (envelope-from ) id 1kLZKd-0003xI-Ij; Fri, 25 Sep 2020 00:03:15 +0200 Received: from [178.196.57.75] (helo=pc-9.home) by sslproxy01.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1kLZKd-000MM3-CP; Fri, 25 Sep 2020 00:03:15 +0200 Subject: Re: [PATCH bpf-next 2/6] bpf, net: rework cookie generator as per-cpu one To: Eric Dumazet , ast@kernel.org Cc: john.fastabend@gmail.com, netdev@vger.kernel.org, bpf@vger.kernel.org References: From: Daniel Borkmann Message-ID: Date: Fri, 25 Sep 2020 00:03:14 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.102.4/25937/Thu Sep 24 15:53:11 2020) Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 9/24/20 8:58 PM, Eric Dumazet wrote: > On 9/24/20 8:21 PM, Daniel Borkmann wrote: [...] >> diff --git a/include/linux/cookie.h b/include/linux/cookie.h >> new file mode 100644 >> index 000000000000..2488203dc004 >> --- /dev/null >> +++ b/include/linux/cookie.h >> @@ -0,0 +1,41 @@ >> +/* SPDX-License-Identifier: GPL-2.0 */ >> +#ifndef __LINUX_COOKIE_H >> +#define __LINUX_COOKIE_H >> + >> +#include >> +#include >> + >> +struct gen_cookie { >> + u64 __percpu *local_last; >> + atomic64_t shared_last ____cacheline_aligned_in_smp; >> +}; >> + >> +#define COOKIE_LOCAL_BATCH 4096 >> + >> +#define DEFINE_COOKIE(name) \ >> + static DEFINE_PER_CPU(u64, __##name); \ >> + static struct gen_cookie name = { \ >> + .local_last = &__##name, \ >> + .shared_last = ATOMIC64_INIT(0), \ >> + } >> + >> +static inline u64 gen_cookie_next(struct gen_cookie *gc) >> +{ >> + u64 *local_last = &get_cpu_var(*gc->local_last); >> + u64 val = *local_last; >> + >> + if (__is_defined(CONFIG_SMP) && >> + unlikely((val & (COOKIE_LOCAL_BATCH - 1)) == 0)) { >> + s64 next = atomic64_add_return(COOKIE_LOCAL_BATCH, >> + &gc->shared_last); >> + val = next - COOKIE_LOCAL_BATCH; >> + } >> + val++; >> + if (unlikely(!val)) >> + val++; >> + *local_last = val; >> + put_cpu_var(local_last); >> + return val; > > This is not interrupt safe. > > I think sock_gen_cookie() can be called from interrupt context. > > get_next_ino() is only called from process context, that is what I used get_cpu_var() > and put_cpu_var() Hmm, agree, good point. Need to experiment a bit more .. initial thinking potentially something like the below could do where we fall back to atomic counter iff we encounter nesting (which should be an extremely rare case normally). BPF progs where this can be called from are non-preemptible, so we could actually move the temp preempt_disable/enable() from get/put_cpu_var() into a wrapper func for slow path non-BPF users as well. static inline u64 gen_cookie_next(struct gen_cookie *gc) { u64 val; if (likely(this_cpu_inc_return(*gc->level_nesting) == 1)) { u64 *local_last = this_cpu_ptr(gc->local_last); val = *local_last; if (__is_defined(CONFIG_SMP) && unlikely((val & (COOKIE_LOCAL_BATCH - 1)) == 0)) { s64 next = atomic64_add_return(COOKIE_LOCAL_BATCH, &gc->shared_last); val = next - COOKIE_LOCAL_BATCH; } val++; if (unlikely(!val)) val++; *local_last = val; } else { val = atomic64_add_return(COOKIE_LOCAL_BATCH, &gc->shared_last); } this_cpu_dec(*gc->level_nesting); return val; } Thanks, Daniel