From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753597AbeAQVth (ORCPT ); Wed, 17 Jan 2018 16:49:37 -0500 Received: from shards.monkeyblade.net ([184.105.139.130]:37550 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752746AbeAQVtg (ORCPT ); Wed, 17 Jan 2018 16:49:36 -0500 Date: Wed, 17 Jan 2018 16:49:32 -0500 (EST) Message-Id: <20180117.164932.1269304606476934540.davem@davemloft.net> To: torvalds@linux-foundation.org Cc: efault@gmx.de, peterz@infradead.org, edumazet@google.com, dima@arista.com, frederic@kernel.org, linux-kernel@vger.kernel.org, 0x7f454c46@gmail.com, akpm@linux-foundation.org, fweisbec@gmail.com, hannes@stressinduktion.org, mingo@kernel.org, alexander.levin@verizon.com, pabeni@redhat.com, paulmck@linux.vnet.ibm.com, rrendec@arista.com, riel@redhat.com, sgruszka@redhat.com, tglx@linutronix.de, wanpeng.li@hotmail.com Subject: Re: [RFC 1/2] softirq: Defer net rx/tx processing to ksoftirqd context From: David Miller In-Reply-To: References: <1515782670.7007.3.camel@gmx.de> <20180117.153049.1803664333084879932.davem@davemloft.net> X-Mailer: Mew version 6.7 on Emacs 25.3 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Linus Torvalds Date: Wed, 17 Jan 2018 13:06:58 -0800 > It was in some way always a "poor mans interrupt thread" (with no > blocking like a real thread context, but at least not impacting actual > interrupt latency). Or in this loopback device case (and tunnel decapsulation) a poor man's longjmp, releasing the current stack frame to keep the depth in check. Anyways... > That said, this made me wonder a bit. I wonder how bounded the latency > is for raising a softirq from process context. We only _check_ the > softirq on the last hardirq exit, I think. System call return checks it, otherwise this situation would be completely bolixed. > I wonder if we should run softirqs on return to user mode (and make > softirq set a thread flag if not in interrupt context). I'm pretty sure we already do.