From nobody Sun Feb 8 07:26:54 2026 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 47C9B3B9611; Thu, 8 Jan 2026 10:14:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767867293; cv=none; b=FMqsluaEEuJ4x9m7Pkgi6cHo3KFdffg39LLGRnJA3SOuiFrcucsKxCrz3KhSUpqjZ7OowLCn4M2TnVWatJy3BrxXjt9vW0jJMGl2stcvsoouRxPKF7enWB1p5vjnX8o8mX6IGoJ7CJixQxRR/y0UhKR9Y0WT1gP/lIia4QJLk4M= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767867293; c=relaxed/simple; bh=cdN6u1hQnjHMGTIOY6Dsnz+u1WCcInE+EjrZCKRddpE=; h=Message-ID:Subject:From:To:Cc:Date:Content-Type:MIME-Version; b=m1H7HviZyaQ3N+PZNgyTbCBLeROJRHPnca7WNxB+EDSedClFoDSCGl58GWPsUlV7w4rzjHx+dWD6gHypRsIViP3Z9Ja86KKefnznCVUwWSbnAgS3f0ptcdXvlFlAekWOLokCbX+0yhhn7v0eyK4sfeAl5Q2Dg/zhOhAk1ExwZHU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=desiato.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=ol8wschj; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=desiato.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="ol8wschj" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=MIME-Version:Content-Type:Date:Cc:To: From:Subject:Message-ID:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:In-Reply-To:References; bh=i+N4sk3wnWYYbPLtXDv58Rb6I8bfhY6IhK0tQvVN8r0=; b=ol8wschjooQhMsLhQEm1JUlhBD 8qaqDUWd+U65J+kBg/yXfN6PoC+V+8jv48CjNh+hCSsMH36AKcqZtO+5GwHdVal6CZX+KqRQmu1Kq gyZTr9qSIwJ+Ufi4vnt60VByTciNXXU2acNzwg49nvTW0O9GlogHDKJP8X2y5eDROe2EJs5hHMZuR lUDerMzJYgbOU8z4dCcYw50jYpULyjjJr3Gmlzx1mWkx1SICBB4zyuUPuN69NprHjK4lzE1cL7yMU ATVKwjaZdpfB8D8+s5SC1q/Ymsrg1Z6PVC1JnRFrXhUfOLTGyISC/bvyg3K6bSvbrqrPXFA2rI5wJ lW+X8lbg==; Received: from [15.248.2.252] (helo=u09cd745991455d.ant.amazon.com) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vdn29-0000000Cu8K-168G; Thu, 08 Jan 2026 10:14:26 +0000 Message-ID: <0d0b7fe70e6dfa7979cb83b05317deb21187f74d.camel@infradead.org> Subject: [PATCH] perf/core: Speed up kexec shutdown by avoiding unnecessary cross CPU calls From: David Woodhouse To: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Cc: "Jan H." =?ISO-8859-1?Q?Sch=F6nherr?= Date: Thu, 08 Jan 2026 11:14:24 +0100 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-6ZsaShl7bA3C6wTAULir" User-Agent: Evolution 3.52.3-0ubuntu1.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html --=-6ZsaShl7bA3C6wTAULir Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" From: Jan H. Sch=C3=B6nherr There are typically a lot of PMUs registered, but in many cases only few of them have an event registered (like the "cpu" PMU in the presence of the watchdog). As the mutex is already held, it's safe to just check for existing events before doing the cross CPU call. This change saves tens of milliseconds from kexec time (perceived as steal time during a hypervisor host update), with <2ms remaining for this step in the shutdown. There might be additional potential for parallelization or we could just disable performance monitoring during the actual shutdown and be less graceful about it. Signed-off-by: Jan H. Sch=C3=B6nherr Signed-off-by: David Woodhouse --- kernel/events/core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 413b88a4e00f..e36372b3c83f 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -14712,7 +14712,8 @@ static void perf_event_exit_cpu_context(int cpu) ctx =3D &cpuctx->ctx; =20 mutex_lock(&ctx->mutex); - smp_call_function_single(cpu, __perf_event_exit_context, ctx, 1); + if (ctx->nr_events) + smp_call_function_single(cpu, __perf_event_exit_context, ctx, 1); cpuctx->online =3D 0; mutex_unlock(&ctx->mutex); mutex_unlock(&pmus_lock); --=20 2.43.0 --=-6ZsaShl7bA3C6wTAULir Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT 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