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 51F4FE92716 for ; Thu, 5 Oct 2023 16:03:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235433AbjJEQCw (ORCPT ); Thu, 5 Oct 2023 12:02:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40514 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237631AbjJEQBM (ORCPT ); Thu, 5 Oct 2023 12:01:12 -0400 Received: from mgamail.intel.com (mgamail.intel.com [134.134.136.126]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 339362D4B for ; Thu, 5 Oct 2023 06:50:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1696513854; x=1728049854; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version; bh=7cLwqKiXl9KfzXnflp8oVp0nz4eFfG4OmGWuM2JBzIs=; b=WxCDvX4m82tFxDRTHzzHNBEhUCRQujuzHmBqQxGU7edfElv+/Kz8qLhA WNgIcPhgF+Nh7OeQE3rsdPAwp/5NSV4y7ikeh6qdsgMyTInpL6SYBJ4Et eq6FLuTIygR0cGQLT4mx1GJf6Yn6sM+qhQegTHG5aX6DXaC/6FFouCXGN nLhFdYceAMJx564N6s6BijnYL+SbDj83re4JSgxsqj3IEvoWfbDpLH0Fj gLY+8koM1IdqS8w6g2FKJbCes7/0lTBPzssTHS29H8rLuf4PNP0Wr2Ils d+ad75VRqNJjXXWRq8F6e5yo5W7WSADyPaQePqRNBmsM6RGbx0F8XU/pd w==; X-IronPort-AV: E=McAfee;i="6600,9927,10853"; a="368534710" X-IronPort-AV: E=Sophos;i="6.03,202,1694761200"; d="scan'208";a="368534710" Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Oct 2023 03:22:21 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10853"; a="822066068" X-IronPort-AV: E=Sophos;i="6.03,202,1694761200"; d="scan'208";a="822066068" Received: from icoveix-mobl1.ger.corp.intel.com (HELO localhost) ([10.252.55.203]) by fmsmga004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Oct 2023 03:22:17 -0700 From: Jani Nikula To: Uros Bizjak , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Daniel Vetter Subject: Re: [PATCH] drm/i915/pmu: Use local64_try_cmpxchg in i915_pmu_event_read In-Reply-To: <20230703150859.6176-1-ubizjak@gmail.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo References: <20230703150859.6176-1-ubizjak@gmail.com> Date: Thu, 05 Oct 2023 13:22:15 +0300 Message-ID: <87ttr5cqso.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 03 Jul 2023, Uros Bizjak wrote: > Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) == old > in i915_pmu_event_read. x86 CMPXCHG instruction returns success in ZF flag, > so this change saves a compare after cmpxchg (and related move instruction > in front of cmpxchg). > > Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg > fails. There is no need to re-read the value in the loop. > > No functional change intended. > > Cc: Jani Nikula > Cc: Joonas Lahtinen > Cc: Rodrigo Vivi > Cc: Tvrtko Ursulin > Cc: David Airlie > Cc: Daniel Vetter > Signed-off-by: Uros Bizjak > --- > drivers/gpu/drm/i915/i915_pmu.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c > index d35973b41186..108b675088ba 100644 > --- a/drivers/gpu/drm/i915/i915_pmu.c > +++ b/drivers/gpu/drm/i915/i915_pmu.c > @@ -696,12 +696,11 @@ static void i915_pmu_event_read(struct perf_event *event) > event->hw.state = PERF_HES_STOPPED; > return; > } > -again: > - prev = local64_read(&hwc->prev_count); > - new = __i915_pmu_event_read(event); > > - if (local64_cmpxchg(&hwc->prev_count, prev, new) != prev) > - goto again; > + prev = local64_read(&hwc->prev_count); > + do { > + new = __i915_pmu_event_read(event); > + } while (!local64_try_cmpxchg(&hwc->prev_count, &prev, new)); Chased through the documentation again, and pushed to drm-intel-next. Thanks for the patch. BR, Jani. > > local64_add(new - prev, &event->count); > } -- Jani Nikula, Intel