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Tue, 14 Jun 2022 09:13:20 -0700 (PDT) Date: Tue, 14 Jun 2022 17:13:16 +0100 From: Mark Rutland To: Peter Zijlstra Subject: Re: [PATCH 15/36] cpuidle,cpu_pm: Remove RCU fiddling from cpu_pm_{enter,exit}() Message-ID: References: <20220608142723.103523089@infradead.org> <20220608144516.871305980@infradead.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220608144516.871305980@infradead.org> Cc: juri.lelli@redhat.com, rafael@kernel.org, benh@kernel.crashing.org, linus.walleij@linaro.org, bsegall@google.com, guoren@kernel.org, pavel@ucw.cz, agordeev@linux.ibm.com, linux-arch@vger.kernel.org, vincent.guittot@linaro.org, mpe@ellerman.id.au, chenhuacai@kernel.org, linux-acpi@vger.kernel.org, agross@kernel.org, geert@linux-m68k.org, linux-imx@nxp.com, catalin.marinas@arm.com, xen-devel@lists.xenproject.org, mattst88@gmail.com, mturquette@baylibre.com, sammy@sammy.net, pmladek@suse.com, linux-pm@vger.kernel.org, jiangshanlai@gmail.com, Sascha Hauer , linux-um@lists.infradead.org, acme@kernel.org, tglx@linutronix.de, linux-omap@vger.kernel.org, dietmar.eggemann@arm.com, rth@twiddle.net, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, senozhatsky@chromium.org, svens@linux.ibm.com, jolsa@kernel.org, paulus@samba.org, linux-ia64@vger.kernel.org, dave.hansen@linux.intel.com, virtualization@lists.linux-foundation.org, James.Bottomley@HansenPartnership.com, jcmvbkbc@gmail.com, thierry.reding@gmail.com, kernel@xen0n.name, quic_neeraju@quicinc.com, linux-s390@vger.kernel.org, vschneid@redhat.com, john.ogness@linutronix.de, ysato@users.sourceforge.jp, linux-sh@vger.kernel.org, festevam@gmail.com, deller@gmx.de, daniel.lezcano@linaro.org, jonathanh@nvidia.com, mathieu.desnoyers@efficios.com, frederic@kernel.org, lenb@kernel.org, linux-xtensa@linux-xtensa.org, kernel@pengutronix.de, gor@linux.ibm.com, linux-arm-msm@vger.kernel.org, linux-alpha@vger.kernel.org, linux-m68k@lists.linux-m68k.org, shorne@gmail.com, linux-arm-kernel@lists.infradead.org, chris@zankel.net, sboyd@kernel.org, dinguyen@kernel.org, bristot@redhat.com, alexander.shishkin@linux.intel.com, lpieralisi@kernel.org, linux@rasmusvillemoes.dk, joel@joelfernandes.org, will@kernel.org, boris.ostrovsky@oracle.com, khilman@kernel.org, linux-csky@vger.kernel.org, pv-drivers@vmware.com, linux-snps-arc@lists.infradead.org, mgorman@suse.de, jacob.jun.pan@linux.intel.com, Arnd Bergmann , ulli.kroll@googlemail.com, vgupta@kernel.org, linux-clk@vger.kernel.org, josh@joshtriplett.org, rostedt@goodmis.org, rcu@vger.kernel.org, bp@alien8.de, bcain@quicinc.com, tsbogend@alpha.franken.de, linux-parisc@vger.kernel.org, sudeep.holla@arm.com, shawnguo@kernel.org, davem@davemloft.net, dalias@libc.org, tony@atomide.com, amakhalov@vmware.com, bjorn.andersson@linaro.org, hpa@zytor.com, sparclinux@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-riscv@lists.infradead.org, anton.ivanov@cambridgegreys.com, jonas@southpole.se, yury.norov@gmail.com, richard@nod.at, x86@kernel.org, linux@armlinux.org.uk, mingo@redhat.com, aou@eecs.berkeley.edu, paulmck@kernel.org, hca@linux.ibm.com, stefan.kristiansson@saunalahti.fi, openrisc@lists.librecores.org, paul.walmsley@sifive.com, linux-tegra@vger.kernel.org, namhyung@kernel.org, andriy.shevchenko@linux.intel.com, jpoimboe@kernel.org, jgross@suse.com, monstr@monstr.eu, linux-mips@vger.kernel.org, palmer@dabbelt.com, anup@brainfault.org, ink@jurassic.park.msu.ru, johannes@sipsolutions.net, linuxppc-dev@lists.ozlabs.org X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Wed, Jun 08, 2022 at 04:27:38PM +0200, Peter Zijlstra wrote: > All callers should still have RCU enabled. IIUC with that true we should be able to drop the RCU_NONIDLE() from drivers/perf/arm_pmu.c, as we only needed that for an invocation via a pm notifier. I should be able to give that a spin on some hardware. > > Signed-off-by: Peter Zijlstra (Intel) > --- > kernel/cpu_pm.c | 9 --------- > 1 file changed, 9 deletions(-) > > --- a/kernel/cpu_pm.c > +++ b/kernel/cpu_pm.c > @@ -30,16 +30,9 @@ static int cpu_pm_notify(enum cpu_pm_eve > { > int ret; > > - /* > - * This introduces a RCU read critical section, which could be > - * disfunctional in cpu idle. Copy RCU_NONIDLE code to let RCU know > - * this. > - */ > - rcu_irq_enter_irqson(); > rcu_read_lock(); > ret = raw_notifier_call_chain(&cpu_pm_notifier.chain, event, NULL); > rcu_read_unlock(); > - rcu_irq_exit_irqson(); To make this easier to debug, is it worth adding an assertion that RCU is watching here? e.g. RCU_LOCKDEP_WARN(!rcu_is_watching(), "cpu_pm_notify() used illegally from EQS"); > > return notifier_to_errno(ret); > } > @@ -49,11 +42,9 @@ static int cpu_pm_notify_robust(enum cpu > unsigned long flags; > int ret; > > - rcu_irq_enter_irqson(); > raw_spin_lock_irqsave(&cpu_pm_notifier.lock, flags); > ret = raw_notifier_call_chain_robust(&cpu_pm_notifier.chain, event_up, event_down, NULL); > raw_spin_unlock_irqrestore(&cpu_pm_notifier.lock, flags); > - rcu_irq_exit_irqson(); ... and likewise here? Thanks, Mark. > > return notifier_to_errno(ret); > } > > _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization