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Tue, 22 Nov 2022 08:05:09 -0800 (PST) MIME-Version: 1.0 References: <20220919095939.761690562@infradead.org> <20220919101521.139727471@infradead.org> In-Reply-To: From: Ulf Hansson Date: Tue, 22 Nov 2022 17:04:33 +0100 Message-ID: Subject: Re: [PATCH v2 12/44] cpuidle,dt: Push RCU-idle into driver To: Peter Zijlstra Cc: juri.lelli@redhat.com, rafael@kernel.org, catalin.marinas@arm.com, 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, christophe.leroy@csgroup.eu, linux-acpi@vger.kernel.org, agross@kernel.org, geert@linux-m68k.org, linux-imx@nxp.com, vgupta@kernel.org, mattst88@gmail.com, mturquette@baylibre.com, sammy@sammy.net, pmladek@suse.com, linux-pm@vger.kernel.org, Sascha Hauer , linux-um@lists.infradead.org, npiggin@gmail.com, tglx@linutronix.de, linux-omap@vger.kernel.org, dietmar.eggemann@arm.com, andreyknvl@gmail.com, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, senozhatsky@chromium.org, svens@linux.ibm.com, jolsa@kernel.org, tj@kernel.org, Andrew Morton , mark.rutland@arm.com, 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, cl@linux.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, dennis@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, loongarch@lists.linux.dev, shorne@gmail.com, chris@zankel.net, sboyd@kernel.org, dinguyen@kernel.org, bristot@redhat.com, alexander.shishkin@linux.intel.com, fweisbec@gmail.com, lpieralisi@kernel.org, atishp@atishpatra.org, linux@rasmusvillemoes.dk, kasan-dev@googlegroups.com, 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, linux-clk@vger.kernel.org, rostedt@goodmis.org, ink@jurassic.park.msu.ru, bcain@quicinc.com, tsbogend@alpha.franken.de, linux-parisc@vger.kernel.org, ryabinin.a.a@gmail.com, sudeep.holla@arm.com, shawnguo@kernel.org, davem@davemloft.net, dalias@libc.org, tony@atomide.com, amakhalov@vmware.com, konrad.dybcio@somainline.org, bjorn.andersson@linaro.org, glider@google.com, hpa@zytor.com, sparclinux@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-riscv@lists.infradead.org, vincenzo.frascino@arm.com, 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, hca@linux.ibm.com, richard.henderson@linaro.org, stefan.kristiansson@saunalahti.fi, openrisc@lists.librecores.org, acme@kernel.org, paul.walmsley@sifive.com, linux-tegra@vger.kernel.org, namhyung@kernel.org, andriy.shevchenko@linux.intel.com, jpoimboe@kernel.org, dvyukov@google.com, jgross@suse.com, monstr@monstr.eu, linux-mips@vger.kernel.org, palmer@dabbelt.com, anup@brainfault.org, bp@alien8.de, johannes@sipsolutions.net, linuxppc-dev@lists.ozlabs.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-sh@vger.kernel.org On Wed, 16 Nov 2022 at 16:29, Peter Zijlstra wrote: > > > Sorry; things keep getting in the way of finishing this :/ > > As such, I need a bit of time to get on-track again.. > > On Tue, Oct 04, 2022 at 01:03:57PM +0200, Ulf Hansson wrote: > > > > --- a/drivers/acpi/processor_idle.c > > > +++ b/drivers/acpi/processor_idle.c > > > @@ -1200,6 +1200,8 @@ static int acpi_processor_setup_lpi_stat > > > state->target_residency = lpi->min_residency; > > > if (lpi->arch_flags) > > > state->flags |= CPUIDLE_FLAG_TIMER_STOP; > > > + if (lpi->entry_method == ACPI_CSTATE_FFH) > > > + state->flags |= CPUIDLE_FLAG_RCU_IDLE; > > > > I assume the state index here will never be 0? > > > > If not, it may lead to that acpi_processor_ffh_lpi_enter() may trigger > > CPU_PM_CPU_IDLE_ENTER_PARAM() to call ct_cpuidle_enter|exit() for an > > idle-state that doesn't have the CPUIDLE_FLAG_RCU_IDLE bit set. > > I'm not quite sure I see how. AFAICT this condition above implies > acpi_processor_ffh_lpi_enter() gets called, no? > > Which in turn is an unconditional __CPU_PM_CPU_IDLE_ENTER() user, so > even if idx==0, it ends up in ct_idle_{enter,exit}(). Seems like I was overlooking something here, you are right, this shouldn't really be a problem. > > > > > > state->enter = acpi_idle_lpi_enter; > > > drv->safe_state_index = i; > > > } > > > --- a/drivers/cpuidle/cpuidle-arm.c > > > +++ b/drivers/cpuidle/cpuidle-arm.c > > > @@ -53,6 +53,7 @@ static struct cpuidle_driver arm_idle_dr > > > * handler for idle state index 0. > > > */ > > > .states[0] = { > > > + .flags = CPUIDLE_FLAG_RCU_IDLE, > > > > Comparing arm64 and arm32 idle-states/idle-drivers, the $subject > > series ends up setting the CPUIDLE_FLAG_RCU_IDLE for the ARM WFI idle > > state (state zero), but only for the arm64 and psci cases (mostly > > arm64). For arm32 we would need to update the ARM_CPUIDLE_WFI_STATE > > too, as that is what most arm32 idle-drivers are using. My point is, > > the code becomes a bit inconsistent. > > True. > > > Perhaps it's easier to avoid setting the CPUIDLE_FLAG_RCU_IDLE bit for > > all of the ARM WFI idle states, for both arm64 and arm32? > > As per the below? > > > > > > .enter = arm_enter_idle_state, > > > .exit_latency = 1, > > > .target_residency = 1, > > > > --- a/include/linux/cpuidle.h > > > +++ b/include/linux/cpuidle.h > > > @@ -282,14 +282,18 @@ extern s64 cpuidle_governor_latency_req( > > > int __ret = 0; \ > > > \ > > > if (!idx) { \ > > > + ct_idle_enter(); \ > > > > According to my comment above, we should then drop these calls to > > ct_idle_enter and ct_idle_exit() here. Right? > > Yes, if we ensure idx==0 never has RCU_IDLE set then these must be > removed. > > > > cpu_do_idle(); \ > > > + ct_idle_exit(); \ > > > return idx; \ > > > } \ > > > \ > > > if (!is_retention) \ > > > __ret = cpu_pm_enter(); \ > > > if (!__ret) { \ > > > + ct_idle_enter(); \ > > > __ret = low_level_idle_enter(state); \ > > > + ct_idle_exit(); \ > > > if (!is_retention) \ > > > cpu_pm_exit(); \ > > > } \ > > > > > So the basic premise is that everything that needs RCU inside the idle > callback must set CPUIDLE_FLAG_RCU_IDLE and by doing that promise to > call ct_idle_{enter,exit}() themselves. > > Setting RCU_IDLE is required when there is RCU usage, however even if > there is no RCU usage, setting RCU_IDLE is fine, as long as > ct_idle_{enter,exit}() then get called. Right, I was thinking that it could make sense to shrink the window for users getting this wrong. In other words, we shouldn't set the CPUIDLE_FLAG_RCU_IDLE unless we really need to. And as I said, consistent behaviour is also nice to have. > > > So does the below (delta) look better to you? Yes, it does! Although, one minor comment below. > > --- a/drivers/acpi/processor_idle.c > +++ b/drivers/acpi/processor_idle.c > @@ -1218,7 +1218,7 @@ static int acpi_processor_setup_lpi_stat > state->target_residency = lpi->min_residency; > if (lpi->arch_flags) > state->flags |= CPUIDLE_FLAG_TIMER_STOP; > - if (lpi->entry_method == ACPI_CSTATE_FFH) > + if (i != 0 && lpi->entry_method == ACPI_CSTATE_FFH) > state->flags |= CPUIDLE_FLAG_RCU_IDLE; > state->enter = acpi_idle_lpi_enter; > drv->safe_state_index = i; > --- a/drivers/cpuidle/cpuidle-arm.c > +++ b/drivers/cpuidle/cpuidle-arm.c > @@ -53,7 +53,7 @@ static struct cpuidle_driver arm_idle_dr > * handler for idle state index 0. > */ > .states[0] = { > - .flags = CPUIDLE_FLAG_RCU_IDLE, > + .flags = 0, Nitpick: I don't think we need to explicitly clear the flag, as it should already be zeroed by the compiler from its static declaration. Right? > .enter = arm_enter_idle_state, > .exit_latency = 1, > .target_residency = 1, > --- a/drivers/cpuidle/cpuidle-psci.c > +++ b/drivers/cpuidle/cpuidle-psci.c > @@ -357,7 +357,7 @@ static int psci_idle_init_cpu(struct dev > * PSCI idle states relies on architectural WFI to be represented as > * state index 0. > */ > - drv->states[0].flags = CPUIDLE_FLAG_RCU_IDLE; > + drv->states[0].flags = 0; > drv->states[0].enter = psci_enter_idle_state; > drv->states[0].exit_latency = 1; > drv->states[0].target_residency = 1; > --- a/drivers/cpuidle/cpuidle-qcom-spm.c > +++ b/drivers/cpuidle/cpuidle-qcom-spm.c > @@ -72,7 +72,7 @@ static struct cpuidle_driver qcom_spm_id > .owner = THIS_MODULE, > .states[0] = { > .enter = spm_enter_idle_state, > - .flags = CPUIDLE_FLAG_RCU_IDLE, > + .flags = 0, > .exit_latency = 1, > .target_residency = 1, > .power_usage = UINT_MAX, > --- a/drivers/cpuidle/cpuidle-riscv-sbi.c > +++ b/drivers/cpuidle/cpuidle-riscv-sbi.c > @@ -337,7 +337,7 @@ static int sbi_cpuidle_init_cpu(struct d > drv->cpumask = (struct cpumask *)cpumask_of(cpu); > > /* RISC-V architectural WFI to be represented as state index 0. */ > - drv->states[0].flags = CPUIDLE_FLAG_RCU_IDLE; > + drv->states[0].flags = 0; > drv->states[0].enter = sbi_cpuidle_enter_state; > drv->states[0].exit_latency = 1; > drv->states[0].target_residency = 1; > --- a/include/linux/cpuidle.h > +++ b/include/linux/cpuidle.h > @@ -282,9 +282,7 @@ extern s64 cpuidle_governor_latency_req( > int __ret = 0; \ > \ > if (!idx) { \ > - ct_idle_enter(); \ > cpu_do_idle(); \ > - ct_idle_exit(); \ > return idx; \ > } \ > \ Kind regards Uffe