From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 14 Jun 2022 18:58:30 +0200 From: Peter Zijlstra Subject: Re: [PATCH 00/36] cpuidle,rcu: Cleanup the mess Message-ID: References: <20220608142723.103523089@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: To: Mark Rutland Cc: rth@twiddle.net, ink@jurassic.park.msu.ru, mattst88@gmail.com, vgupta@kernel.org, linux@armlinux.org.uk, ulli.kroll@googlemail.com, linus.walleij@linaro.org, shawnguo@kernel.org, Sascha Hauer , kernel@pengutronix.de, festevam@gmail.com, linux-imx@nxp.com, tony@atomide.com, khilman@kernel.org, catalin.marinas@arm.com, will@kernel.org, guoren@kernel.org, bcain@quicinc.com, chenhuacai@kernel.org, kernel@xen0n.name, geert@linux-m68k.org, sammy@sammy.net, monstr@monstr.eu, tsbogend@alpha.franken.de, dinguyen@kernel.org, jonas@southpole.se, stefan.kristiansson@saunalahti.fi, shorne@gmail.com, James.Bottomley@hansenpartnership.com, deller@gmx.de, mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@samba.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, ysato@users.sourceforge.jp, dalias@libc.org, davem@davemloft.net, richard@nod.at, anton.ivanov@cambridgegreys.com, johannes@sipsolutions.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@kernel.org, namhyung@kernel.org, jgross@suse.com, srivatsa@csail.mit.edu, amakhalov@vmware.com, pv-drivers@vmware.com, boris.ostrovsky@oracle.com, chris@zankel.net, jcmvbkbc@gmail.com, rafael@kernel.org, lenb@kernel.org, pavel@ucw.cz, gregkh@linuxfoundation.org, mturquette@baylibre.com, sboyd@kernel.org, daniel.lezcano@linaro.org, lpieralisi@kernel.org, sudeep.holla@arm.com, agross@kernel.org, bjorn.andersson@linaro.org, anup@brainfault.org, thierry.reding@gmail.com, jonathanh@nvidia.com, jacob.jun.pan@linux.intel.com, Arnd Bergmann , yury.norov@gmail.com, andriy.shevchenko@linux.intel.com, linux@rasmusvillemoes.dk, rostedt@goodmis.org, pmladek@suse.com, senozhatsky@chromium.org, john.ogness@linutronix.de, paulmck@kernel.org, frederic@kernel.org, quic_neeraju@quicinc.com, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, joel@joelfernandes.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, jpoimboe@kernel.org, linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-omap@vger.kernel.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, openrisc@lists.librecores.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org, linux-perf-users@vger.kernel.org, virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, linux-xtensa@linux-xtensa.org, linux-acpi@vger.kernel.org, linux-pm@vger.kernel.org, linux-clk@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-tegra@vger.kernel.org, linux-arch@vger.kernel.org, rcu@vger.kernel.org List-ID: On Tue, Jun 14, 2022 at 12:19:29PM +0100, Mark Rutland wrote: > On Wed, Jun 08, 2022 at 04:27:23PM +0200, Peter Zijlstra wrote: > > Hi All! (omg so many) > > Hi Peter, > > Sorry for the delay; my plate has also been rather full recently. I'm beginning > to page this in now. No worries; we all have too much to do ;-) > > These here few patches mostly clear out the utter mess that is cpuidle vs rcuidle. > > > > At the end of the ride there's only 2 real RCU_NONIDLE() users left > > > > arch/arm64/kernel/suspend.c: RCU_NONIDLE(__cpu_suspend_exit()); > > drivers/perf/arm_pmu.c: RCU_NONIDLE(armpmu_start(event, PERF_EF_RELOAD)); > > The latter of these is necessary because apparently PM notifiers are called > with RCU not watching. Is that still the case today (or at the end of this > series)? If so, that feels like fertile land for more issues (yaey...). If not, > we should be able to drop this. That should be fixed; fingers crossed :-) > > kernel/cfi.c: RCU_NONIDLE({ > > > > (the CFI one is likely dead in the kCFI rewrite) and there's only a hand full > > of trace_.*_rcuidle() left: > > > > kernel/trace/trace_preemptirq.c: trace_irq_enable_rcuidle(CALLER_ADDR0, CALLER_ADDR1); > > kernel/trace/trace_preemptirq.c: trace_irq_disable_rcuidle(CALLER_ADDR0, CALLER_ADDR1); > > kernel/trace/trace_preemptirq.c: trace_irq_enable_rcuidle(CALLER_ADDR0, caller_addr); > > kernel/trace/trace_preemptirq.c: trace_irq_disable_rcuidle(CALLER_ADDR0, caller_addr); > > kernel/trace/trace_preemptirq.c: trace_preempt_enable_rcuidle(a0, a1); > > kernel/trace/trace_preemptirq.c: trace_preempt_disable_rcuidle(a0, a1); > > > > All of them are in 'deprecated' code that is unused for GENERIC_ENTRY. > > I think those are also unused on arm64 too? > > If not, I can go attack that. My grep spots: arch/arm64/kernel/entry-common.c: trace_hardirqs_on(); arch/arm64/include/asm/daifflags.h: trace_hardirqs_off(); arch/arm64/include/asm/daifflags.h: trace_hardirqs_off(); The _on thing should be replaced with something like: trace_hardirqs_on_prepare(); lockdep_hardirqs_on_prepare(); instrumentation_end(); rcu_irq_exit(); lockdep_hardirqs_on(CALLER_ADDR0); (as I think you know, since you have some of that already). And something similar for the _off thing, but with _off_finish(). > > I've touched a _lot_ of code that I can't test and likely broken some of it :/ > > In particular, the whole ARM cpuidle stuff was quite involved with OMAP being > > the absolute 'winner'. > > > > I'm hoping Mark can help me sort the remaining ARM64 bits as he moves that to > > GENERIC_ENTRY. > > Moving to GENERIC_ENTRY as a whole is going to take a tonne of work > (refactoring both arm64 and the generic portion to be more amenable to each > other), but we can certainly move closer to that for the bits that matter here. I know ... been there etc.. :-) > Maybe we want a STRICT_ENTRY option to get rid of all the deprecated stuff that > we can select regardless of GENERIC_ENTRY to make that easier. Possible yeah. > > I've also got a note that says ARM64 can probably do a WFE based > > idle state and employ TIF_POLLING_NRFLAG to avoid some IPIs. > > Possibly; I'm not sure how much of a win that'll be given that by default we'll > have a ~10KHz WFE wakeup from the timer, but we could take a peek. Ohh.. I didn't know it woke up *that* often. I just know Will made use of it in things like smp_cond_load_relaxed() which would be somewhat similar to a very shallow idle state that looks at the TIF word.