From patchwork Mon Jul 3 15:08:18 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Uros Bizjak X-Patchwork-Id: 13300541 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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 63B27EB64DC for ; Mon, 3 Jul 2023 23:16:30 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 1F16310E254; Mon, 3 Jul 2023 23:16:27 +0000 (UTC) Received: from mail-lf1-x129.google.com (mail-lf1-x129.google.com [IPv6:2a00:1450:4864:20::129]) by gabe.freedesktop.org (Postfix) with ESMTPS id 9552C10E05D; Mon, 3 Jul 2023 15:09:12 +0000 (UTC) Received: by mail-lf1-x129.google.com with SMTP id 2adb3069b0e04-4fba86f069bso3854518e87.3; Mon, 03 Jul 2023 08:09:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1688396950; x=1690988950; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=ZM6qVqvWt1I2BgabBjdwqk9L05J50In8hCGZpzZU0J8=; b=b4xu7CCdz/dJ76lzYoo3GkzuOZXURVVPrZRgnBNDR+Vp8AONZQTt3U8J+xte9czkNV gVrmLYSs2/wJANfJ9wDikHfdTXUsCN4bVEIQg64fRiUC3pcbLZbs+nPYhgiCAVtMj508 5NY9oA4bAj1zkyF8oGJH7mhrmBYeRDg8mVvo9uqIDPMqwAf6u3PV2t2g2GUlUM1PaLWo dH9mwjsKm18Ddzn0dAspR0LEyw65rwwdms7WffPGVLYqhSkRBepiTP8L1xqisnN7piAd gf5qYr4y3p813lvb53RhfzTDpyGym6xLpRPBEab25KVr44mZLgQyFaX3qtpoAJase4dc addw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1688396950; x=1690988950; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=ZM6qVqvWt1I2BgabBjdwqk9L05J50In8hCGZpzZU0J8=; b=JvjZWhrvAYb+fReMwQBRYdcPR1kbmUx4eFi6QnS9SIQIyw16IDw8mxyrpxjao9r4V+ kZpMhMxediDobPPA73aqXz4qAeRAQPdthNoD0vGYldX5ykkTaSVgqgL7IC8LIktyms37 7h0JAKr7Fh9XmxQKbzvc7NMMcBkjNMjSHNFjz+LFj8kSz2xQVnUJHrPLG1yumI0N0oma Kr5qxYP+dAjIAtbg7FfSi1/FWMu9PZCft3Z/q3eYDP+92qvwKsmtgK2aw/RoRRS9Gt9c sBIcgG0xH6cd52nvNp62gCimsyMBcizuwcpvu5p1qgMVxN9/xueco7jxFvfYb96qipnO +r9g== X-Gm-Message-State: ABy/qLanGZ6u5kzF+2QaYleL+E/8o/9ETY2zNH2bdpScQckvmReI7cVx AYJ8+ZUTqKbQH5KwFl0Ts7GBxW7fXoLzoWEI X-Google-Smtp-Source: APBJJlE3KQ1SG6ccqPBqxmI7ZwNLWnW7syZsJMoLOXEaVktd3RA/EmCt+g+H/mifRRMLmWz9uB+jhQ== X-Received: by 2002:ac2:58fb:0:b0:4fb:9772:6639 with SMTP id v27-20020ac258fb000000b004fb97726639mr6466708lfo.6.1688396950214; Mon, 03 Jul 2023 08:09:10 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id e8-20020a1709062c0800b009786c8249d6sm12221211ejh.175.2023.07.03.08.09.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Jul 2023 08:09:09 -0700 (PDT) From: Uros Bizjak To: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: [PATCH] drm/i915/pmu: Use local64_try_cmpxchg in i915_pmu_event_read Date: Mon, 3 Jul 2023 17:08:18 +0200 Message-ID: <20230703150859.6176-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.41.0 MIME-Version: 1.0 X-Mailman-Approved-At: Mon, 03 Jul 2023 23:16:23 +0000 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Tvrtko Ursulin , Uros Bizjak , Rodrigo Vivi Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" 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)); local64_add(new - prev, &event->count); }