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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, T_DKIMWL_WL_HIGH 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 3B969C43142 for ; Thu, 2 Aug 2018 15:19:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E3C3621525 for ; Thu, 2 Aug 2018 15:19:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="HFGg0RD5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E3C3621525 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=arista.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387683AbeHBRK7 (ORCPT ); Thu, 2 Aug 2018 13:10:59 -0400 Received: from mail-ed1-f68.google.com ([209.85.208.68]:33781 "EHLO mail-ed1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387456AbeHBRK7 (ORCPT ); Thu, 2 Aug 2018 13:10:59 -0400 Received: by mail-ed1-f68.google.com with SMTP id x5-v6so1093557edr.0 for ; Thu, 02 Aug 2018 08:19:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=arista.com; s=googlenew; h=message-id:subject:from:to:cc:date:in-reply-to:references :mime-version:content-transfer-encoding; bh=FtBjHKBRWCTND0nq29zdYttazcwXXmGJgqYkpmhpM60=; b=HFGg0RD5Fj6clhPSUOZd/4T3XzAISnjU0+RNDwI4X7L5EY9d/zFCOZcVohV0eA5frZ mV95S0jgBwaVBCfORJqO/PmMBiQNn9kCxuDhmL/PN5MQufrKJ8j8yDPRTPkWzcn75vY5 5bywSrzksk5otuACjqFE1AhbcSp0h8TpRKBG9H6aT4mnCFzEOXTniwEuUm2ClKCl/fp7 i03QyzsnQpX0iuc08rvxW1F6I6gVRYasKuRBtesesX0ku52SHXe1z6ZNt7f9O7P2/vMB eBSe1fTiy/E+BzFrjMFNzpwSAk5384jvhrk3UK6lBRe6hYz6kLBtL8Jo3Fgf+Z9r1+Zu ZX+w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:message-id:subject:from:to:cc:date:in-reply-to :references:mime-version:content-transfer-encoding; bh=FtBjHKBRWCTND0nq29zdYttazcwXXmGJgqYkpmhpM60=; b=UNHFX/vI/5u3t33n95JdDpeVZzFkYTpNAPngcmRH8IsnxwAypJdc8r2fBq3pdIl3Ey sRXRV3Lm3LkRw64Bas1dSr9TZjFxx+VxbyHEYwFG1d7I/NjTs4i+8Lv65C5T4wAINz0l Wax59YPqv+TwNgfWOyJBTyUHBKyCzxwTCUsqJarSFi/sWmxy1CYOMiCbWBUVgk8oDhTQ UnTXtlX5uT8I5Tlznxf/qeaEvL8TWF7gOKW6/n8vogpaPFaMa/8Op9TJ/utbSkKeNvf5 rEzRNSri2Ugr3k7xCbZlWHIm07q2p1zPe+0oaJpNK3PgGQ+QIN9TYzPJVcsobLW4ImDb 50mg== X-Gm-Message-State: AOUpUlFBYT/daE/kINA1+LLMeIThc8DY3vKUth/8zL/BgRmRUykQ0wRE QM3RLJ28Wyi9Cv7iC3F4VO9hZw== X-Google-Smtp-Source: AAOMgpdyED36QLv8abxDILBk2cS1GVpv7p3xgtVHN9Qr3qMUKM3R+01Zb6gCEZJkgYtcjeS+xJhu+w== X-Received: by 2002:a50:9069:: with SMTP id z38-v6mr3855999edz.79.1533223160091; Thu, 02 Aug 2018 08:19:20 -0700 (PDT) Received: from dhcp.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id c25-v6sm865750edt.54.2018.08.02.08.19.15 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 02 Aug 2018 08:19:16 -0700 (PDT) Message-ID: <1533223155.2679.136.camel@arista.com> Subject: Re: [PATCHv3] lib/ratelimit: Lockless ratelimiting From: Dmitry Safonov To: Steven Rostedt Cc: Petr Mladek , Andy Shevchenko , Linux Kernel Mailing List , Arnd Bergmann , David Airlie , Greg Kroah-Hartman , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Theodore Ts'o , Thomas Gleixner , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org Date: Thu, 02 Aug 2018 16:19:15 +0100 In-Reply-To: <20180801214855.3ae1abb9@vmware.local.home> References: <20180703225628.25684-1-dima@arista.com> <1531789154.18720.3.camel@arista.com> <20180720150948.nv57fjmmrmo2r7rx@pathway.suse.cz> <1532100816.18720.44.camel@arista.com> <20180801214855.3ae1abb9@vmware.local.home> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.24.6 (3.24.6-1.fc26) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Steven, Thanks for your reply, On Wed, 2018-08-01 at 21:48 -0400, Steven Rostedt wrote: > I'm just catching up from my vacation. What about making rs->missed > into an atomic, and have: > > if (!raw_spin_trylock_irqsave(&rs->lock, flags)) { > atomic_inc(&rs->missed); > return 0; > } > > ? Uhm. Do you mean as a preparation patch to split this on two patches? Because it will not solve the issue where one CPU has taken rs->lock, and is updating rs->printed, checking burst and whatnot; while the second CPU will loose the message which was even *under* burst limit. I.e.: there are enough of printk_ratelimit() users in tree and a message from one can be suppressed, while shouldn't. > You would also need to do: > > if (time_is_before_jiffies(rs->begin + rs->interval)) { > int missed = atomic_xchg(&rs->missed, 0); > if (missed) { > > So that you don't have a race between checking rs->missed and setting > it > to zero. -- Thanks, Dmitry