Messages in this thread | | | Subject | Re: [PATCH v4] ACPI/processor_idle: Remove dummy wait if kernel is in guest | From | "Yin, Fengwei" <> | Date | Fri, 25 Oct 2019 17:59:36 +0800 |
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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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