2020-10-24 19:54:16

by Chen Yu

Subject: [PATCH] intel_idle: Fix max_cstate for processor models without C-state tables

Currently intel_idle driver gets the c-state information from ACPI
_CST if the processor model is not recognized by it. However the
c-state in _CST starts with index 1 which is different from the
index in intel_idle driver's internal c-state table. While
intel_idle_max_cstate_reached() was previously introduced to
deal with intel_idle driver's internal c-state table, re-using
this function directly on _CST might get wrong. Fix this by
subtracting the index by 1 when checking max cstate via _CST.
For example, append intel_idle.max_cstate=1 in boot command line,
Before the patch:
grep . /sys/devices/system/cpu/cpu0/cpuidle/state*/name
POLL
After the patch:
grep . /sys/devices/system/cpu/cpu0/cpuidle/state*/name
/sys/devices/system/cpu/cpu0/cpuidle/state0/name:POLL
/sys/devices/system/cpu/cpu0/cpuidle/state1/name:C1_ACPI

Fixes: 18734958e9bf ("intel_idle: Use ACPI _CST for processor models without C-state tables")
Reported-by: Pengfei Xu <[email protected]>
Cc: 5.6+ <[email protected]> # 5.6+
Signed-off-by: Chen Yu <[email protected]>
---
drivers/idle/intel_idle.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 9a810e4a7946..dbd4be1c271b 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -1236,7 +1236,7 @@ static void __init intel_idle_init_cstates_acpi(struct cpuidle_driver *drv)
struct acpi_processor_cx *cx;
struct cpuidle_state *state;

- if (intel_idle_max_cstate_reached(cstate))
+ if (intel_idle_max_cstate_reached(cstate - 1))
break;

cx = &acpi_state_table.states[cstate];
--
2.17.1

2020-10-28 18:26:02

by Rafael J. Wysocki

Subject: Re: [PATCH] intel_idle: Fix max_cstate for processor models without C-state tables

On Sat, Oct 24, 2020 at 6:27 PM Chen Yu <[email protected]> wrote:
>
> Currently intel_idle driver gets the c-state information from ACPI
> _CST if the processor model is not recognized by it. However the
> c-state in _CST starts with index 1 which is different from the
> index in intel_idle driver's internal c-state table. While
> intel_idle_max_cstate_reached() was previously introduced to
> deal with intel_idle driver's internal c-state table, re-using
> this function directly on _CST might get wrong. Fix this by
> subtracting the index by 1 when checking max cstate via _CST.
> For example, append intel_idle.max_cstate=1 in boot command line,
> Before the patch:
> grep . /sys/devices/system/cpu/cpu0/cpuidle/state*/name
> POLL
> After the patch:
> grep . /sys/devices/system/cpu/cpu0/cpuidle/state*/name
> /sys/devices/system/cpu/cpu0/cpuidle/state0/name:POLL
> /sys/devices/system/cpu/cpu0/cpuidle/state1/name:C1_ACPI
>
> Fixes: 18734958e9bf ("intel_idle: Use ACPI _CST for processor models without C-state tables")
> Reported-by: Pengfei Xu <[email protected]>
> Cc: 5.6+ <[email protected]> # 5.6+
> Signed-off-by: Chen Yu <[email protected]>
> ---
> drivers/idle/intel_idle.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> index 9a810e4a7946..dbd4be1c271b 100644
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -1236,7 +1236,7 @@ static void __init intel_idle_init_cstates_acpi(struct cpuidle_driver *drv)
> struct acpi_processor_cx *cx;
> struct cpuidle_state *state;
>
> - if (intel_idle_max_cstate_reached(cstate))
> + if (intel_idle_max_cstate_reached(cstate - 1))
> break;
>
> cx = &acpi_state_table.states[cstate];
> --

Applied as 5.10-rc material with some changelog edits, thanks!