From patchwork Tue Jun 7 07:50:57 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Zqiang X-Patchwork-Id: 12871483 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 37F2CC43334 for ; Tue, 7 Jun 2022 07:51:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230296AbiFGHvN (ORCPT ); Tue, 7 Jun 2022 03:51:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34072 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229930AbiFGHvM (ORCPT ); Tue, 7 Jun 2022 03:51:12 -0400 Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0ADE6C9664; Tue, 7 Jun 2022 00:51:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1654588270; x=1686124270; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=uK91ZcW1W7x+yvwxlB6uEa0V46hkzdc1gVduu3AMBJA=; b=GiLLI+0492aCiXaGYLkvYFSzIvGspTrsSwNeu3a+wsCL+5BRcaK349uu fzsCBBFgKck6Kt/44nB+cSBQU5JDSWadz/yMvaT17eDiWogXfnx7pBuF2 CPxVBXGhvfUS7ipTG7t2qKmXbq2rTuXX2Gm1F7nBmCL5ec+eg/fBfSKLd p3M8hVOECBuE5yw6aNkATQTksMCZfZjJjbPKdrmc876d5ekQamTpXlXSV Zc5njEU6PF3vUNbK8kFwy8EySqqd29XhgQ1KMLq0UHHm96jgom01AuhLu /ItMgy+4LmlZomNq7DI99KIPVyrJYUn5sP9FrZ23WpOz95Rqt/wb9Uyrs g==; X-IronPort-AV: E=McAfee;i="6400,9594,10370"; a="363054959" X-IronPort-AV: E=Sophos;i="5.91,283,1647327600"; d="scan'208";a="363054959" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Jun 2022 00:51:09 -0700 X-IronPort-AV: E=Sophos;i="5.91,283,1647327600"; d="scan'208";a="636008143" Received: from zq-optiplex-7090.bj.intel.com ([10.238.156.125]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Jun 2022 00:51:08 -0700 From: Zqiang To: paulmck@kernel.org, frederic@kernel.org Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] rcu/nocb: Avoid polling when myrdp->nocb_head_rdp list is empty Date: Tue, 7 Jun 2022 15:50:57 +0800 Message-Id: <20220607075057.909070-1-qiang1.zhang@intel.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Currently, If the 'rcu_nocb_poll' bootargs is enable, all rcuog kthreads enter polling mode. however, due to only insert CPU's rdp which belong to rcu_nocb_mask to 'nocb_head_rdp' list or all CPU's rdp served by rcuog kthread have been de-offloaded, these cause the 'nocb_head_rdp' list served by rcuog kthread is empty, when the 'nocb_head_rdp' is empty, the rcuog kthread in polling mode not actually do anything. fix it by exiting polling mode when the 'nocb_head_rdp'list is empty, otherwise entering polling mode. Signed-off-by: Zqiang --- v1->v2: Move rcu_nocb_poll flags check from rdp_offload_toggle() to rcu_nocb_rdp_offload/deoffload(), avoid unnecessary setting of rdp_gp->nocb_gp_sleep flags, because when rcu_nocb_poll is set the rdp_gp->nocb_gp_sleep is not used. kernel/rcu/tree_nocb.h | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index fa8e4f82e60c..2a52c9abc681 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -698,10 +698,14 @@ static void nocb_gp_wait(struct rcu_data *my_rdp) TPS("WakeBypassIsDeferred")); } if (rcu_nocb_poll) { - /* Polling, so trace if first poll in the series. */ - if (gotcbs) - trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll")); - schedule_timeout_idle(1); + if (list_empty(&my_rdp->nocb_head_rdp)) { + rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp)); + } else { + /* Polling, so trace if first poll in the series. */ + if (gotcbs) + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll")); + schedule_timeout_idle(1); + } } else if (!needwait_gp) { /* Wait for callbacks to appear. */ trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep")); @@ -1030,7 +1034,7 @@ static long rcu_nocb_rdp_deoffload(void *arg) mutex_lock(&rdp_gp->nocb_gp_kthread_mutex); if (rdp_gp->nocb_gp_kthread) { - if (wake_gp) + if (wake_gp || rcu_nocb_poll) wake_up_process(rdp_gp->nocb_gp_kthread); /* @@ -1152,7 +1156,7 @@ static long rcu_nocb_rdp_offload(void *arg) * rcu_nocb_unlock() rcu_nocb_unlock() */ wake_gp = rdp_offload_toggle(rdp, true, flags); - if (wake_gp) + if (wake_gp || rcu_nocb_poll) wake_up_process(rdp_gp->nocb_gp_kthread); swait_event_exclusive(rdp->nocb_state_wq, rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) &&