From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v2 12/44] cpuidle,dt: Push RCU-idle into driver Date: Wed, 16 Nov 2022 16:29:05 +0100 Message-ID: References: <20220919095939.761690562@infradead.org> <20220919101521.139727471@infradead.org> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=4XDB6ZbR3Awa7mOslon9xFqMWj0psrdiARhozQeRyJA=; b=gYnS7fY4SiIk8LhruYi5TSnTVA fStgfkd5Z/zbz8yQZBnmnhyWOOmhlrhRObDB9G2KJoco51LBuhZxVkVxbSBrTCQ/HtHWliung+7ZZ HbZe3Froz8dQdsOphMI16X4jllstvINRTH3i5h+4adnzIV8bwm2odcxdw/4ACLq7NTIENgyfmZxmW flqbgkCx8yOd3LgZHd01MR5R1P5lI3CSROlGEycIvrRPVhabpLUb0rptouTmOLEERLT81z+aE6Z4G +eccUWkk2tCLQB+FJ0eM8fcpEENqemtpoKisOMtzDEaLdPH2PhfiSrDXw+vDx7DBnwdyTpMo06laG hxV51fpA==; Content-Disposition: inline In-Reply-To: List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Ulf Hansson 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.or 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}(). > > > 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. So does the below (delta) look better to you? --- 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, .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; \ } \ \