From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH RT 3.18] irq_work: Provide a soft-irq based queue Date: Fri, 24 Apr 2015 11:00:29 +0200 Message-ID: <553A062D.6090608@siemens.com> References: <552FC1FE.4020406@siemens.com> <552FC6B1.1040000@linutronix.de> <552FC72A.8060709@siemens.com> <20150416111041.66043164@gandalf.local.home> <552FD55F.8000105@siemens.com> <552FE320.6050601@siemens.com> <1429517036.3226.9.camel@gmail.com> <1429769505.3419.9.camel@gmail.com> <55389632.50308@siemens.com> <1429772482.3419.40.camel@gmail.com> <55389B67.3000703@siemens.com> <1429773566.3419.42.camel@gmail.com> <20150423170026.0de65c90@gandalf.local.home> <1429858489.3461.28.camel@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Sebastian Andrzej Siewior , RT , Linux Kernel Mailing List To: Mike Galbraith , Steven Rostedt Return-path: In-Reply-To: <1429858489.3461.28.camel@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org On 2015-04-24 08:54, Mike Galbraith wrote: > On Thu, 2015-04-23 at 17:00 -0400, Steven Rostedt wrote: >> On Thu, 23 Apr 2015 09:19:26 +0200 >> Mike Galbraith wrote: >> >>>> CC kernel/irq_work.o >>>> In file included from ../include/asm-generic/percpu.h:6:0, >>>> from ../arch/x86/include/asm/percpu.h:522, >>>> from ../arch/x86/include/asm/current.h:5, >>>> from ../arch/x86/include/asm/processor.h:15, >>>> from ../arch/x86/include/asm/irq_work.h:4, >>>> from ../include/linux/irq_work.h:47, >>>> from ../kernel/irq_work.c:11: >>>> ../kernel/irq_work.c: In function =E2=80=98irq_work_queue_on=E2=80= =99: >>>> ../kernel/irq_work.c:85:17: error: =E2=80=98hirq_work_list=E2=80=99= undeclared=20 >>>> (first use in this function) >>>> &per_cpu(hirq_work_list, cpu)); >>> >>> Aw poo, so that's just what I _thought_ it was for. >> >> It helps optimization but does nothing for undefined symbols. >> >> That said, why don't we clean up that irq_work code and at least >> declare both lists, and get rid of all the #ifdefs. I wonder if gcc = is >> smart enough to not allocate a static variable if it happens to be >> optimized out? >=20 > Nope, it didn't notice a thing. >=20 > This is a stab at that cleanup. Usable as is with Jan's ok, or as > fodder for your bitmaster-9000 patch shredder, or whatever. Box work= s > and it makes line count shrink... >=20 > I downgraded evolution v3.16->v3.12 to restore its ability to read it= 's > own fscking "Preformatted" switch, so whitespace should be fine.=20 >=20 > Oh, btw, if anyone (else) makes a 4.1-rt, your rt push work will want > one of those nifty hirq tags lest box make boom due to trying to do t= hat > not only way late, but with irqs enabled which pisses sched all off. >=20 > Subject: [PATCH RT 3.18] irq_work: Provide a soft-irq based queue > Date: Thu, 16 Apr 2015 18:28:16 +0200 > From: Jan Kiszka >=20 > Instead of turning all irq_work requests into lazy ones on -rt, just > move their execution from hard into soft-irq context. >=20 > This resolves deadlocks of ftrace which will queue work from arbitrar= y > contexts, including those that have locks held that are needed for > raising a soft-irq. >=20 > Mike: cleanup ifdef mess and kill hirq_work_list. We need two lists, > and already have them, merely need to select according to work type. > In -rt all work not tagged for hirq execution is queued to the lazy > list and runs via irq_work_tick(). Raising SOFTIRQ_TIMER is always > done via IPI for deadlock safety, if the work item is not a lazy work > or the tick is stopped, fire IPI immediately, otherwise let it wait. > IOW, lazy work is lazy in -rt only until someone queues immediate wor= k. The approach looks good to me, but the commit log deserves a rework now= =2E Jan --=20 Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux