From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:43529 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751153AbbEBRp0 (ORCPT ); Sat, 2 May 2015 13:45:26 -0400 Subject: Patch "ksoftirqd: Enable IRQs and call cond_resched() before poking RCU" has been added to the 3.10-stable tree To: calvinowens@fb.com, gregkh@linuxfoundation.org, mgalbraith@suse.de, paulmck@linux.vnet.ibm.com Cc: , From: Date: Sat, 02 May 2015 19:44:52 +0200 Message-ID: <143058869210962@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled ksoftirqd: Enable IRQs and call cond_resched() before poking RCU to the 3.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ksoftirqd-enable-irqs-and-call-cond_resched-before-poking-rcu.patch and it can be found in the queue-3.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 28423ad283d5348793b0c45cc9b1af058e776fd6 Mon Sep 17 00:00:00 2001 From: Calvin Owens Date: Tue, 13 Jan 2015 13:16:18 -0800 Subject: ksoftirqd: Enable IRQs and call cond_resched() before poking RCU 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 @@ -774,9 +774,13 @@ static void run_ksoftirqd(unsigned int c 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(); Patches currently in stable-queue which might be from calvinowens@fb.com are queue-3.10/ksoftirqd-enable-irqs-and-call-cond_resched-before-poking-rcu.patch