From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: Softirq priority inversion from "softirq: reduce latencies" Date: Sat, 27 Feb 2016 15:33:58 -0800 Message-ID: <56D23266.2080306@hurleysoftware.com> References: <56D1E8B6.6090003@hurleysoftware.com> <1456604037.648.29.camel@edumazet-ThinkPad-T530> <56D20733.1000409@hurleysoftware.com> <20160227.180403.2101360385050644823.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: eric.dumazet@gmail.com, edumazet@google.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org, dmaengine@vger.kernel.org, john.ogness@linutronix.de, bigeasy@linutronix.de, akpm@linux-foundation.org To: David Miller Return-path: In-Reply-To: <20160227.180403.2101360385050644823.davem@davemloft.net> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 02/27/2016 03:04 PM, David Miller wrote: > From: Peter Hurley > Date: Sat, 27 Feb 2016 12:29:39 -0800 > >> Not really. softirq raised from interrupt context will always execute >> on this cpu and not in ksoftirqd, unless load forces softirq loop abort. > > That guarantee never was specified. ?? Neither is running network socket servers at normal priority as if they're higher priority than softirq. > Or are you saying that by design, on a system under load, your UART > will not function properly? > > Surely you don't mean that. No, that's not what I mean. What I mean is that bypassing the entire SOFTIRQ priority so that sshd can process one network packet makes a mockery of the point of softirq. This hack to workaround NET_RX looping over-and-over-and-over affects every subsystem, not just one uart. HI, TIMER, BLOCK; all of these are skipped: that's straight-up, a bug. Regards, Peter Hurley