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SubjectRe: [PATCH v4] ACPI/processor_idle: Remove dummy wait if kernel is in guest
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On 10/25/2019 5:06 PM, Rafael J. Wysocki wrote:
> On Thu, Oct 24, 2019 at 9:04 AM Yin Fengwei <fengwei.yin@intel.com> wrote:
>>
>> In function acpi_idle_do_entry(), an ioport access is used for
>> dummy wait to guarantee hardware behavior. But it could trigger
>> unnecessary VMexit if kernel is running as guest in virtualization
>> environment.
>>
>> If it's in virtualization environment, the deeper C state enter
>> operation (inb()) will trap to hypervisor. It's not needed to do
>> dummy wait after the inb() call. So we could just remove the
>> dummy io port access to avoid unnecessary VMexit.
>>
>> And keep dummy io port access to maintain timing for native
>> environment.
>>
>> Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
>> ---
>> ChangeLog:
>> v3 -> v4:
>> - Drop overengineered function pointer and do check whether
>> we are in guest before dummy inl call.
>>
>> v2 -> v3:
>> - Remove dummy io port access totally for virtualization env.
>>
>> v1 -> v2:
>> - Use ndelay instead of dead loop for dummy delay.
>>
>> drivers/acpi/processor_idle.c | 21 +++++++++++++++------
>> 1 file changed, 15 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
>> index ed56c6d20b08..2ae95df2e74f 100644
>> --- a/drivers/acpi/processor_idle.c
>> +++ b/drivers/acpi/processor_idle.c
>> @@ -642,6 +642,19 @@ static int acpi_idle_bm_check(void)
>> return bm_status;
>> }
>>
>> +static void wait_for_freeze(void)
>> +{
>> +#ifdef CONFIG_X86
>> + /* No delay is needed if we are in guest */
>> + if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
>> + return;
>> +#endif
>> + /* Dummy wait op - must do something useless after P_LVL2 read
>> + because chipsets cannot guarantee that STPCLK# signal
>> + gets asserted in time to freeze execution properly. */
>> + inl(acpi_gbl_FADT.xpm_timer_block.address);
>> +}
>> +
>> /**
>> * acpi_idle_do_entry - enter idle state using the appropriate method
>> * @cx: cstate data
>> @@ -658,10 +671,7 @@ static void __cpuidle acpi_idle_do_entry(struct acpi_processor_cx *cx)
>> } else {
>> /* IO port based C-state */
>> inb(cx->address);
>> - /* Dummy wait op - must do something useless after P_LVL2 read
>> - because chipsets cannot guarantee that STPCLK# signal
>> - gets asserted in time to freeze execution properly. */
>> - inl(acpi_gbl_FADT.xpm_timer_block.address);
>> + wait_for_freeze();
>> }
>> }
>>
>> @@ -682,8 +692,7 @@ static int acpi_idle_play_dead(struct cpuidle_device *dev, int index)
>> safe_halt();
>> else if (cx->entry_method == ACPI_CSTATE_SYSTEMIO) {
>> inb(cx->address);
>> - /* See comment in acpi_idle_do_entry() */
>> - inl(acpi_gbl_FADT.xpm_timer_block.address);
>> + wait_for_freeze();
>> } else
>> return -ENODEV;
>> }
>> --
>
> Applying as 5.5 material, thanks!
Thanks a lot.

Regards
Yin, Fengwei

>

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