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=-3.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 E30F6C5518A for ; Fri, 24 Apr 2020 03:59:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BCC7220767 for ; Fri, 24 Apr 2020 03:59:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="PanBHZdv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726423AbgDXD7z (ORCPT ); Thu, 23 Apr 2020 23:59:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57300 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1725922AbgDXD7z (ORCPT ); Thu, 23 Apr 2020 23:59:55 -0400 Received: from mail-pl1-x641.google.com (mail-pl1-x641.google.com [IPv6:2607:f8b0:4864:20::641]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 400C6C09B045 for ; Thu, 23 Apr 2020 20:59:55 -0700 (PDT) Received: by mail-pl1-x641.google.com with SMTP id d24so3262461pll.8 for ; Thu, 23 Apr 2020 20:59:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=mime-version:content-transfer-encoding:in-reply-to:references :subject:from:cc:to:date:message-id:user-agent; bh=OUVxQF+oC0mlk6FQJe7RPNH97fg6Os38vM17nA7u2v4=; b=PanBHZdvJgcCE2sQEDbfNptEXd2LoewP/cdztrIQJ8zsMm7qBCJ4rb14rKRxckCuIi AkWLmrJwNMNwrrgknZ0p7Pe1Iet4XcWd5s2P1CYKGT9f/LtHoWlNU46SiDWtTAuxOwAC 3ggB+LyQNWc3vrRj14PUJVKS6IJJRgvGdtr2c= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:content-transfer-encoding :in-reply-to:references:subject:from:cc:to:date:message-id :user-agent; bh=OUVxQF+oC0mlk6FQJe7RPNH97fg6Os38vM17nA7u2v4=; b=o5REcCDNrbNln2qM04/6Rit2IbJM+tNZQWPtnlL3YDjbQiQPeiWgIb4y53wpAmjtfk rSdGhXBtwQtkRoL79b+DvwQ3t9HCnZ11C4EYyYpUhFWiPk4VFSvEY/de4k2O8uwXtXND uwkOt1iWQdAR8EBLKOxcEbSbpLHso47fvrFCaf5KpnnAk19KDYX7Fhb7oLZ9WthwSlmV p9f+C+v+d2yJJEG8j6D8Cee707sXbWPxSLUBn12CJUV8/mST7I/JtCyQWT8Rta+Zztu6 bXkrIwp1nZ1kkOr7ZbVHcA21hfYKBsX5b4eCU5TzifB1mjsUnZYxC5Zan+am1taT9VqG UiKw== X-Gm-Message-State: AGi0PuarU4VD44hRRNkdiVTDV9XdB5GMj/2QizOjXfdzLFgJ7i3RNQZJ GtRrerFaBEo4Hh2LHW3P/qCevg== X-Google-Smtp-Source: APiQypIfk8zyw99IbqgvbDJNXYALRVLhuXlRSJ7PIl3u+1588Xj4XFdbySV/wfLt2qod8HEst3vl+g== X-Received: by 2002:a17:90a:25cb:: with SMTP id k69mr4076138pje.93.1587700794708; Thu, 23 Apr 2020 20:59:54 -0700 (PDT) Received: from chromium.org ([2620:15c:202:1:fa53:7765:582b:82b9]) by smtp.gmail.com with ESMTPSA id c3sm3662204pjc.43.2020.04.23.20.59.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Apr 2020 20:59:53 -0700 (PDT) Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable In-Reply-To: <20200422145408.v4.5.I295cb72bc5334a2af80313cbe97cb5c9dcb1442c@changeid> References: <20200422145408.v4.1.Ic7096b3b9b7828cdd41cd5469a6dee5eb6abf549@changeid> <20200422145408.v4.5.I295cb72bc5334a2af80313cbe97cb5c9dcb1442c@changeid> Subject: Re: [PATCH v4 5/5] soc: qcom: rpmh-rsc: Remove the pm_lock From: Stephen Boyd Cc: mka@chromium.org, mkshah@codeaurora.org, evgreen@chromium.org, Douglas Anderson , linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org To: Andy Gross , Bjorn Andersson , Douglas Anderson , Greg Kroah-Hartman , rafael.j.wysocki@intel.com Date: Thu, 23 Apr 2020 20:59:52 -0700 Message-ID: <158770079266.135303.7831640949542355577@swboyd.mtv.corp.google.com> User-Agent: alot/0.9 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Quoting Douglas Anderson (2020-04-22 14:55:03) > It has been postulated that the pm_lock is bad for performance because > a CPU currently running rpmh_flush() could block other CPUs from > coming out of idle. Similarly CPUs coming out of / going into idle > all need to contend with each other for the spinlock just to update > the variable tracking who's in PM. >=20 > Let's optimize this a bit. Specifically: >=20 > - Use a count rather than a bitmask. This is faster to access and > also means we can use the atomic_inc_return() function to really > detect who the last one to enter PM was. > - Accept that it's OK if we race and are doing the flush (because we > think we're last) while another CPU is coming out of idle. As long > as we block that CPU if/when it tries to do an active-only transfer > we're OK. >=20 > Signed-off-by: Douglas Anderson > --- Reviewed-by: Stephen Boyd