Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946437AbbEPIFv (ORCPT ); Sat, 16 May 2015 04:05:51 -0400 Received: from bband-dyn183.178-41-215.t-com.sk ([178.41.215.183]:22466 "EHLO ip4-83-240-18-248.cust.nbox.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1030295AbbEPIFg (ORCPT ); Sat, 16 May 2015 04:05:36 -0400 From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Calvin Owens , "Paul E. McKenney" , Mike Galbraith , Jiri Slaby Subject: [PATCH 3.12 073/142] ksoftirqd: Enable IRQs and call cond_resched() before poking RCU Date: Sat, 16 May 2015 09:37:13 +0200 Message-Id: <4e75ff4f0985418801dd55d90208dcf989f3c9fd.1431761807.git.jslaby@suse.cz> X-Mailer: git-send-email 2.3.7 In-Reply-To: <70c3d4ae1322b9e9bd7443ef574af5635234a0fa.1431761807.git.jslaby@suse.cz> References: <70c3d4ae1322b9e9bd7443ef574af5635234a0fa.1431761807.git.jslaby@suse.cz> In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1970 Lines: 60 From: Calvin Owens 3.12-stable review patch. If anyone has any objections, please let me know. =============== 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: Jiri Slaby --- kernel/softirq.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index d7d498d8cc4f..b331c8756543 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -772,9 +772,13 @@ static void run_ksoftirqd(unsigned int cpu) local_irq_disable(); if (local_softirq_pending()) { __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(); -- 2.3.7 -- 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/