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 D6ACDC7EE2E for ; Fri, 9 Jun 2023 19:44:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231924AbjFIToD (ORCPT ); Fri, 9 Jun 2023 15:44:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45278 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229517AbjFIToB (ORCPT ); Fri, 9 Jun 2023 15:44:01 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BA2D53590 for ; Fri, 9 Jun 2023 12:43:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1686339791; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=hsFhpgfxWMykwSn5/1ALxRTTekNl16jpPv5u3IzbyUM=; b=WnfU2RbJZsIkCS/V1OIp4QtN/BG1SCWt0XKV3/YZY7xEnSSXIiQjTujaOfBMSiZKIvL5qZ J6/1CMvvnEgGtWicGN6WQO+GCF8+4SapJG89+KuleSZ8Tgdfp0tUm/nkLVXXu1uFkjpg7U wHdkjMrqa9T8BGYJD1s90eMFU9aXxaE= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-185-v63rzh51PMKQAlWrLVjzEg-1; Fri, 09 Jun 2023 15:43:06 -0400 X-MC-Unique: v63rzh51PMKQAlWrLVjzEg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D05FD101A52C; Fri, 9 Jun 2023 19:43:05 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 74E7840C1438; Fri, 9 Jun 2023 19:43:05 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id 42AE1401030E9; Fri, 9 Jun 2023 10:54:04 -0300 (-03) Date: Fri, 9 Jun 2023 10:54:04 -0300 From: Marcelo Tosatti To: Peter Zijlstra Cc: Frederic Weisbecker , "Rafael J. Wysocki" , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched/idle: disable tick in idle=poll idle entry Message-ID: References: <20230608083400.GH998233@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230608083400.GH998233@hirez.programming.kicks-ass.net> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 08, 2023 at 10:34:00AM +0200, Peter Zijlstra wrote: > On Wed, Jun 07, 2023 at 10:10:46PM -0300, Marcelo Tosatti wrote: > > > > Commit a5183862e76fdc25f36b39c2489b816a5c66e2e5 > > ("tick/nohz: Conditionally restart tick on idle exit") allows > > a nohz_full CPU to enter idle and return from it with the > > scheduler tick disabled (since the tick might be undesired noise). > > > > The idle=poll case still unconditionally restarts the tick when entering > > idle. > > > > To reduce the noise for that case as well, stop the tick when entering > > idle, for the idle=poll case. > > > > tick_nohz_idle_exit (called if the NEED_RESCHED bit is set) > > is responsible for re-enabling the tick when necessary. > > Who cares and why? Systems that use isolcpus/nohz_full, and use idle=poll to avoid sleeping. For example: https://github.com/intel/FlexRAN/blob/master/README.md More specifically, the case which HLTs (via nanosleep usually) is: https://www.isa.org/intech-home/2022/february-2022/departments/what-you-may-not-know-about-softplcs Can add this to the next version of the patch (unless you have any other comments). Thanks.