From: Sven Joachim <svenjoac@gmx.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: rjw@rjwysocki.net, bp@alien8.de, x86@kernel.org,
tony.luck@intel.com, lenb@kernel.org, daniel.lezcano@linaro.org,
linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org,
linux-pm@vger.kernel.org, ulf.hansson@linaro.org,
paulmck@kernel.org, tglx@linutronix.de,
naresh.kamboju@linaro.org
Subject: Re: [RFC][PATCH 4/4] acpi: Take over RCU-idle for C3-BM idle
Date: Mon, 21 Sep 2020 11:12:33 +0200 [thread overview]
Message-ID: <87wo0npk72.fsf@turtle.gmx.de> (raw)
In-Reply-To: <20200915103806.479637218@infradead.org> (Peter Zijlstra's message of "Tue, 15 Sep 2020 12:32:01 +0200")
On 2020-09-15 12:32 +0200, Peter Zijlstra wrote:
> The C3 BusMaster idle code takes lock in a number of places, some deep
> inside the ACPI code. Instead of wrapping it all in RCU_NONIDLE, have
> the driver take over RCU-idle duty and avoid flipping RCU state back
> and forth a lot.
>
> ( by marking 'C3 && bm_check' as RCU_IDLE, we _must_ call enter_bm() for
> that combination, otherwise we'll loose RCU-idle, this requires
> shuffling some code around )
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
I got modpost errors in 5.9-rc6 after this patch:
ERROR: modpost: "rcu_idle_enter" [drivers/acpi/processor.ko] undefined!
ERROR: modpost: "rcu_idle_exit" [drivers/acpi/processor.ko] undefined!
Reverting commit 1fecfdbb7acc made them go away. Notably my
configuration had CONFIG_ACPI_PROCESSOR=m, changing that
to CONFIG_ACPI_PROCESSOR=y let the build succeed as well.
Cheers,
Sven
> ---
> drivers/acpi/processor_idle.c | 69 +++++++++++++++++++++++++++++-------------
> 1 file changed, 49 insertions(+), 20 deletions(-)
>
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -558,22 +558,43 @@ static DEFINE_RAW_SPINLOCK(c3_lock);
>
> /**
> * acpi_idle_enter_bm - enters C3 with proper BM handling
> + * @drv: cpuidle driver
> * @pr: Target processor
> * @cx: Target state context
> + * @index: index of target state
> */
> -static void acpi_idle_enter_bm(struct acpi_processor *pr,
> - struct acpi_processor_cx *cx)
> +static int acpi_idle_enter_bm(struct cpuidle_driver *drv,
> + struct acpi_processor *pr,
> + struct acpi_processor_cx *cx,
> + int index)
> {
> + static struct acpi_processor_cx safe_cx = {
> + .entry_method = ACPI_CSTATE_HALT,
> + };
> +
> /*
> * disable bus master
> * bm_check implies we need ARB_DIS
> * bm_control implies whether we can do ARB_DIS
> *
> - * That leaves a case where bm_check is set and bm_control is
> - * not set. In that case we cannot do much, we enter C3
> - * without doing anything.
> + * That leaves a case where bm_check is set and bm_control is not set.
> + * In that case we cannot do much, we enter C3 without doing anything.
> */
> - if (pr->flags.bm_control) {
> + bool dis_bm = pr->flags.bm_control;
> +
> + /* If we can skip BM, demote to a safe state. */
> + if (!cx->bm_sts_skip && acpi_idle_bm_check()) {
> + dis_bm = false;
> + index = drv->safe_state_index;
> + if (index >= 0) {
> + cx = this_cpu_read(acpi_cstate[index]);
> + } else {
> + cx = &safe_cx;
> + index = -EBUSY;
> + }
> + }
> +
> + if (dis_bm) {
> raw_spin_lock(&c3_lock);
> c3_cpu_count++;
> /* Disable bus master arbitration when all CPUs are in C3 */
> @@ -582,15 +603,21 @@ static void acpi_idle_enter_bm(struct ac
> raw_spin_unlock(&c3_lock);
> }
>
> + rcu_idle_enter();
> +
> acpi_idle_do_entry(cx);
>
> + rcu_idle_exit();
> +
> /* Re-enable bus master arbitration */
> - if (pr->flags.bm_control) {
> + if (dis_bm) {
> raw_spin_lock(&c3_lock);
> acpi_write_bit_register(ACPI_BITREG_ARB_DISABLE, 0);
> c3_cpu_count--;
> raw_spin_unlock(&c3_lock);
> }
> +
> + return index;
> }
>
> static int acpi_idle_enter(struct cpuidle_device *dev,
> @@ -604,20 +631,13 @@ static int acpi_idle_enter(struct cpuidl
> return -EINVAL;
>
> if (cx->type != ACPI_STATE_C1) {
> + if (cx->type == ACPI_STATE_C3 && pr->flags.bm_check)
> + return acpi_idle_enter_bm(drv, pr, cx, index);
> +
> + /* C2 to C1 demotion. */
> if (acpi_idle_fallback_to_c1(pr) && num_online_cpus() > 1) {
> index = ACPI_IDLE_STATE_START;
> cx = per_cpu(acpi_cstate[index], dev->cpu);
> - } else if (cx->type == ACPI_STATE_C3 && pr->flags.bm_check) {
> - if (cx->bm_sts_skip || !acpi_idle_bm_check()) {
> - acpi_idle_enter_bm(pr, cx);
> - return index;
> - } else if (drv->safe_state_index >= 0) {
> - index = drv->safe_state_index;
> - cx = per_cpu(acpi_cstate[index], dev->cpu);
> - } else {
> - acpi_safe_halt();
> - return -EBUSY;
> - }
> }
> }
>
> @@ -641,7 +661,13 @@ static int acpi_idle_enter_s2idle(struct
> return 0;
>
> if (pr->flags.bm_check) {
> - acpi_idle_enter_bm(pr, cx);
> + u8 bm_sts_skip = cx->bm_sts_skip;
> +
> + /* Don't check BM_STS, do an unconditional ARB_DIS for S2IDLE */
> + cx->bm_sts_skip = 1;
> + acpi_idle_enter_bm(drv, pr, cx, index);
> + cx->bm_sts_skip = bm_sts_skip;
> +
> return 0;
> } else {
> ACPI_FLUSH_CPU_CACHE();
> @@ -674,8 +700,11 @@ static int acpi_processor_setup_cpuidle_
> if (lapic_timer_needs_broadcast(pr, cx))
> state->flags |= CPUIDLE_FLAG_TIMER_STOP;
>
> - if (cx->type == ACPI_STATE_C3)
> + if (cx->type == ACPI_STATE_C3) {
> state->flags |= CPUIDLE_FLAG_TLB_FLUSHED;
> + if (pr->flags.bm_check)
> + state->flags |= CPUIDLE_FLAG_RCU_IDLE;
> + }
>
> count++;
> if (count == CPUIDLE_STATE_MAX)
next prev parent reply other threads:[~2020-09-21 9:18 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-15 10:31 [RFC][PATCH 0/4] Fix up ACPI processor idle vs RCU Peter Zijlstra
2020-09-15 10:31 ` [RFC][PATCH 1/4] acpi: Use CPUIDLE_FLAG_TIMER_STOP Peter Zijlstra
2020-09-15 16:26 ` Rafael J. Wysocki
2020-09-16 15:42 ` peterz
2020-09-16 16:01 ` Borislav Petkov
2020-09-16 17:38 ` Rafael J. Wysocki
2020-09-16 17:38 ` Rafael J. Wysocki
2020-09-22 3:26 ` Guenter Roeck
2020-09-22 19:03 ` Rafael J. Wysocki
2020-09-15 10:31 ` [RFC][PATCH 2/4] acpi: Use CPUIDLE_FLAG_TLB_FLUSHED Peter Zijlstra
2020-09-15 10:32 ` [RFC][PATCH 3/4] cpuidle: Allow cpuidle drivers to take over RCU-idle Peter Zijlstra
2020-09-15 13:20 ` Ulf Hansson
2020-09-15 10:32 ` [RFC][PATCH 4/4] acpi: Take over RCU-idle for C3-BM idle Peter Zijlstra
2020-09-21 9:12 ` Sven Joachim [this message]
2020-09-21 10:37 ` [PATCH] rcu/tree: Export rcu_idle_{enter,exit} to module Borislav Petkov
2020-09-21 12:15 ` Rafael J. Wysocki
2020-09-21 13:32 ` Paul E. McKenney
2020-09-21 13:38 ` Rafael J. Wysocki
2020-09-25 15:20 ` [RFC][PATCH 4/4] acpi: Take over RCU-idle for C3-BM idle Guenter Roeck
2020-09-25 15:24 ` Rafael J. Wysocki
2020-09-25 15:29 ` Paul E. McKenney
2020-09-15 18:31 ` [RFC][PATCH 0/4] Fix up ACPI processor idle vs RCU Borislav Petkov
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