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 A3AD8C77B75 for ; Mon, 8 May 2023 22:32:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234015AbjEHWcC (ORCPT ); Mon, 8 May 2023 18:32:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58544 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233976AbjEHWb7 (ORCPT ); Mon, 8 May 2023 18:31:59 -0400 Received: from mx0b-00069f02.pphosted.com (mx0b-00069f02.pphosted.com [205.220.177.32]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F07A665AA for ; Mon, 8 May 2023 15:31:58 -0700 (PDT) Received: from pps.filterd (m0246632.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 348JOsrS002212; Mon, 8 May 2023 22:31:48 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-transfer-encoding; s=corp-2023-03-30; bh=B9yD/+CYrKVcypcEgjmGEaQX//z09PC+3sHaWn9qNXY=; b=fip0cDRmD8TGviS8pvRKyVtChRoKOPG4Uqplmf2abB2QcojmY1eCz5DLB2pLzNRgncMH uTfDfdYcK21C6QvR3vjRC7L44pFQ1M1vmWusmcg0fUskZe80tf9XSie5VXF9M3MKqYRh KzOBmZQlVz8LcGF1iG/g4LDjmrwF2HsHPB6DIcxxnRWczbxVrpnwgMqdZzV8exidM/Ma k2J+xvWY0tAeFuOEI4BfcSyXV7em+Msee1ed/MT2Luf5LS3PUCeBWkwFphD8wSCdreAd LibmmQPyRerz/Eo/b71/wSANSs1vBLO8IXMLhyE8oT2Zw2P7jB4DOenw7plQ+EWopzIb Gg== Received: from iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (iadpaimrmta01.appoci.oracle.com [130.35.100.223]) by mx0b-00069f02.pphosted.com (PPS) with ESMTPS id 3qf7770ah6-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 08 May 2023 22:31:48 +0000 Received: from pps.filterd (iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com [127.0.0.1]) by iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (8.17.1.19/8.17.1.19) with ESMTP id 348LZuea015246; Mon, 8 May 2023 22:31:48 GMT Received: from localhost.localdomain (dhcp-10-191-130-46.vpn.oracle.com [10.191.130.46]) by iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTP id 3qf77f5pca-3; Mon, 08 May 2023 22:31:47 +0000 From: Imran Khan To: peterz@infradead.org, paulmck@kernel.org, jgross@suse.com, vschneid@redhat.com, yury.norov@gmail.com, tglx@linutronix.de Cc: linux-kernel@vger.kernel.org Subject: [RESEND PATCH 2/2] smp: Reduce NMI traffic from CSD waiters to CSD destination. Date: Tue, 9 May 2023 08:31:24 +1000 Message-Id: <20230508223124.1438167-3-imran.f.khan@oracle.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230508223124.1438167-1-imran.f.khan@oracle.com> References: <20230508223124.1438167-1-imran.f.khan@oracle.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-05-08_16,2023-05-05_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 malwarescore=0 adultscore=0 spamscore=0 mlxscore=0 phishscore=0 bulkscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2304280000 definitions=main-2305080149 X-Proofpoint-GUID: rDEMgUGpwh1Lrqbkr3GQOK8wEb2tQVkb X-Proofpoint-ORIG-GUID: rDEMgUGpwh1Lrqbkr3GQOK8wEb2tQVkb Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On systems with hundreds of CPUs, if few hundred or most of the CPUs detect a CSD hang, then all of these waiters endup sending an NMI to destination CPU to dump its backtrace. Depending on the number of such NMIs, destination CPU can spent a significant amount of time handling these NMIs and thus making it more difficult for this CPU to address those pending CSDs timely. In worst case it can happen that by the time destination CPU is done handling all of the above mentioned backtrace NMIs, csd wait time may have elapsed and all of the waiters start sending backtrace NMI again and this behaviour continues in loop. To avoid the above mentioned scenario, issue backtrace NMI only from first waiter. The other waiters to same CSD destination can make use of backtrace obtained via fist waiter's NMI. Signed-off-by: Imran Khan --- kernel/smp.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/smp.c b/kernel/smp.c index b7ccba677a0a0..a1cd21ea8b308 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -43,6 +43,8 @@ static DEFINE_PER_CPU_ALIGNED(struct call_function_data, cfd_data); static DEFINE_PER_CPU_SHARED_ALIGNED(struct llist_head, call_single_queue); +static DEFINE_PER_CPU(atomic_t, trigger_backtrace) = ATOMIC_INIT(1); + static void __flush_smp_call_function_queue(bool warn_cpu_offline); int smpcfd_prepare_cpu(unsigned int cpu) @@ -242,7 +244,8 @@ static bool csd_lock_wait_toolong(struct __call_single_data *csd, u64 ts0, u64 * *bug_id, !cpu_cur_csd ? "unresponsive" : "handling this request"); } if (cpu >= 0) { - dump_cpu_task(cpu); + if (atomic_cmpxchg_acquire(&per_cpu(trigger_backtrace, cpu), 1, 0)) + dump_cpu_task(cpu); if (!cpu_cur_csd) { pr_alert("csd: Re-sending CSD lock (#%d) IPI from CPU#%02d to CPU#%02d\n", *bug_id, raw_smp_processor_id(), cpu); arch_send_call_function_single_ipi(cpu); @@ -423,9 +426,14 @@ static void __flush_smp_call_function_queue(bool warn_cpu_offline) struct llist_node *entry, *prev; struct llist_head *head; static bool warned; + atomic_t *tbt; lockdep_assert_irqs_disabled(); + /* Allow waiters to send backtrace NMI from here onwards */ + tbt = this_cpu_ptr(&trigger_backtrace); + atomic_set_release(tbt, 1); + head = this_cpu_ptr(&call_single_queue); entry = llist_del_all(head); entry = llist_reverse_order(entry); -- 2.34.1