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=-5.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 DD5B3C4363D for ; Fri, 25 Sep 2020 15:00:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7ECB021D42 for ; Fri, 25 Sep 2020 15:00:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601046023; bh=/hcZrQBk6c3ZUDPJ9tBI/HFhM9gxyHp4Nl9AXMNCJgs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=wHgejqLN/gmdYk1yZuUF89lxUaUiCxJnaSKLnr7+fL3BhVRBvCli1XqkIRYYASeqS AnM+/gA8/41aGWC7d/Z7ignTZfFH9TAH7+9nzS1eZlojejaGgpmsZF06eRII6tBaos Mb6qcOsxW2FR/H07JmvTa/ub/2KDRdR9QgM7B6mM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729205AbgIYPAX (ORCPT ); Fri, 25 Sep 2020 11:00:23 -0400 Received: from mail.kernel.org ([198.145.29.99]:42998 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728333AbgIYPAW (ORCPT ); Fri, 25 Sep 2020 11:00:22 -0400 Received: from kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com (unknown [163.114.132.6]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C9DC820715; Fri, 25 Sep 2020 15:00:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601046022; bh=/hcZrQBk6c3ZUDPJ9tBI/HFhM9gxyHp4Nl9AXMNCJgs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=sOhU9u/AcSHN01u+C/3/rDcW+A1ojw4SWLk62TOJS5W8VgVePr4kF01v+l2kRJWeu APnEQRrnheDgmUunO4gwgU7Jqdp5q5LdCZ3UnUZZ/JGySoH4nWb/7zqA88d7M3bfNW yti6l+T7Wysu7HR2/h8Ir+yj9HsOZZeBPjvlus6M= Date: Fri, 25 Sep 2020 08:00:20 -0700 From: Jakub Kicinski To: Daniel Borkmann Cc: Eric Dumazet , ast@kernel.org, john.fastabend@gmail.com, netdev@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH bpf-next 2/6] bpf, net: rework cookie generator as per-cpu one Message-ID: <20200925080020.013165a0@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, 25 Sep 2020 00:03:14 +0200 Daniel Borkmann wrote: > static inline u64 gen_cookie_next(struct gen_cookie *gc) > { > u64 val; > > if (likely(this_cpu_inc_return(*gc->level_nesting) == 1)) { Is this_cpu_inc() in itself atomic? Is there a comparison of performance of various atomic ops and locking somewhere? I wonder how this scheme would compare to a using a cmpxchg. > u64 *local_last = this_cpu_ptr(gc->local_last); > > val = *local_last; > if (__is_defined(CONFIG_SMP) && > unlikely((val & (COOKIE_LOCAL_BATCH - 1)) == 0)) { Can we reasonably assume we won't have more than 4k CPUs and just statically divide this space by encoding CPU id in top bits? > 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; > }