Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1948642AbbEBTqo (ORCPT ); Sat, 2 May 2015 15:46:44 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:46522 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1947059AbbEBTqi (ORCPT ); Sat, 2 May 2015 15:46:38 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Calvin Owens , "Paul E. McKenney" , Mike Galbraith Subject: [PATCH 3.14 84/92] ksoftirqd: Enable IRQs and call cond_resched() before poking RCU Date: Sat, 2 May 2015 21:03:39 +0200 Message-Id: <20150502190117.866521375@linuxfoundation.org> X-Mailer: git-send-email 2.3.7 In-Reply-To: <20150502190109.683061482@linuxfoundation.org> References: <20150502190109.683061482@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1876 Lines: 57 3.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Calvin Owens commit 28423ad283d5348793b0c45cc9b1af058e776fd6 upstream. While debugging an issue with excessive softirq usage, I encountered the following note in commit 3e339b5dae24a706 ("softirq: Use hotplug thread infrastructure"): [ paulmck: Call rcu_note_context_switch() with interrupts enabled. ] ...but despite this note, the patch still calls RCU with IRQs disabled. This seemingly innocuous change caused a significant regression in softirq CPU usage on the sending side of a large TCP transfer (~1 GB/s): when introducing 0.01% packet loss, the softirq usage would jump to around 25%, spiking as high as 50%. Before the change, the usage would never exceed 5%. Moving the call to rcu_note_context_switch() after the cond_sched() call, as it was originally before the hotplug patch, completely eliminated this problem. Signed-off-by: Calvin Owens Signed-off-by: Paul E. McKenney Signed-off-by: Mike Galbraith Signed-off-by: Greg Kroah-Hartman --- kernel/softirq.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -657,9 +657,13 @@ static void run_ksoftirqd(unsigned int c * in the task stack here. */ __do_softirq(); - rcu_note_context_switch(cpu); local_irq_enable(); cond_resched(); + + preempt_disable(); + rcu_note_context_switch(cpu); + preempt_enable(); + return; } local_irq_enable(); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/