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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 B684DC43381 for ; Fri, 8 Mar 2019 15:30:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 81D292147A for ; Fri, 8 Mar 2019 15:30:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1552059029; bh=LoUNdu8zcrAquYzmh6OQn3jcRuVJq7eYnHHWxd3DBrY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=rkJ+nPXvA1jVPAVmRcbjyI3TC1v8oJfVUXjLzVKc25FAEsxVqbKeAOmEqxEU0oceU 4iA2uzoie4lbOHGYLv6GWz9vbbBsx6tmUnfJouei1RVG7BX3X1Y+B8GY9zP9jJvZXj I+IOMh4sT5f487YukmAY+cyRVOrDoxt+9RMxVh5U= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726639AbfCHPa2 (ORCPT ); Fri, 8 Mar 2019 10:30:28 -0500 Received: from mail.kernel.org ([198.145.29.99]:36768 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725789AbfCHPa1 (ORCPT ); Fri, 8 Mar 2019 10:30:27 -0500 Received: from localhost (lfbn-1-18527-45.w90-101.abo.wanadoo.fr [90.101.69.45]) (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 1908A208E4; Fri, 8 Mar 2019 15:30:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1552059026; bh=LoUNdu8zcrAquYzmh6OQn3jcRuVJq7eYnHHWxd3DBrY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=QJ1JRlBd19WsmnJo6Bj2/bsgSH/3rIQUrHSi+/mR2z9v07+B2Dq+kF+tiyus2JfX+ kA7/MX1WgY6BxYNvGHrJRxpRLU/Huf560AnmqFv0ftSCQrp9ga+09GTZytDqmCYQLn ZbuTgRLhC6M1ljCLXDAhUa9/pDbdysjyRP1Va71c= Date: Fri, 8 Mar 2019 16:30:23 +0100 From: Frederic Weisbecker To: Linus Torvalds Cc: LKML , Sebastian Andrzej Siewior , Peter Zijlstra , "David S . Miller" , Mauro Carvalho Chehab , Thomas Gleixner , "Paul E . McKenney" , Frederic Weisbecker , Pavan Kondeti , Ingo Molnar , Joel Fernandes Subject: Re: [PATCH 00/37] softirq: Per vector masking v3 Message-ID: <20190308153022.GA23080@lenoir> References: <20190228171242.32144-1-frederic@kernel.org> <20190301034536.GA19200@lenoir> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 01, 2019 at 08:51:38AM -0800, Linus Torvalds wrote: > On Thu, Feb 28, 2019 at 7:45 PM Frederic Weisbecker wrote: > > > > Numbers are indeed missing. In fact this patchset mostly just brings an > > infrastructure. We have yet to pinpoint the most latency-inducing > > softirq disabled sites and make them disable only the vectors that > > are involved in a given lock. > > Note that I think we pretty much know that already: the people who > have had issues have never actually really had issues with the actual > "disable softirq" paths, they've all been about actually *running* the > softirq's (and that in turn being a latency issue for running _other_ > softirqs, and in particular for delaying them into softirqd). > > Now, it may well be that yes, we'll have "block softirqs" code that > has issues too, but it's absolutely been swamped by the latencies for > actually running them so far. > > Note that this is all really fairly independent of the whole masking > logic. Yes, the masking logic comes into play too (allowing you to run > a subset of softirq's at a time), but on the whole the complaints I've > seen have not been "the networking softirq takes so long that it > delays USB tasklet handling", but they have been along the lines of > "the networking softirq gets invoked so often that it then floods the > system and triggers softirqd, and _that_ then makes tasklet handling > latency go up insanely". > > See the difference? Not the latency of softirq's disabled, but the > latency of one group of softirqs causing problems for another when > they all get batched together (and soft-scheduled to another context > together). I see, so that's an entirely different problem that vector soft-interruptibility can't fix, at least not alone. The only solution I can imagine is to have a seperate pending mask for normal softirq processing and ksoftirqd, so that only vectors that have been enqueued for threaded processing are delayed. I can work on that first, but I really need to be able to reproduce an example of the issue. The USB capture thing seems to be one the best. Let's browse some history to see if I can find some details on the relevant scenario.