* [PATCH RFC] ACPI: disable extra P_LVLx access on KVM
@ 2018-03-30 17:43 Michael S. Tsirkin
2018-04-23 8:07 ` Rafael J. Wysocki
0 siblings, 1 reply; 3+ messages in thread
From: Michael S. Tsirkin @ 2018-03-30 17:43 UTC (permalink / raw)
To: linux-kernel
Cc: Paolo Bonzini, Radim Krčmář,
kvm, Rafael J. Wysocki, Len Brown, linux-acpi
As documented by commit b488f021 "ACPI: restore comment justifying
'extra' P_LVLx access", Linux does an extra IO read after entering idle
because on (some) chipsets STPCLK# doesn't get asserted in time
to prevent further instruction processing.
This can never be the case on KVM, and a timer read causes an expensive
VM exit in turn causing useless load on host system. Detect KVM and skip
the read. TODO: whitelist more hypervisors?
Note: very lightly tested. Pls don't apply this yet, I am working on a
_CST implementation for KVM and will repost this without the RFC tag
when it's been tested properly.
Posting now for early flames/feedback.
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: kvm@vger.kernel.org
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/acpi/processor_idle.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index abb559c..8ae28dc 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -33,6 +33,7 @@
#include <linux/cpuidle.h>
#include <linux/cpu.h>
#include <acpi/processor.h>
+#include <linux/kvm_para.h>
/*
* Include the apic definitions for x86 to have the APIC timer related defines
@@ -665,7 +666,8 @@ static void __cpuidle acpi_idle_do_entry(struct acpi_processor_cx *cx)
/* 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);
+ if (!kvm_para_available())
+ inl(acpi_gbl_FADT.xpm_timer_block.address);
}
}
@@ -687,7 +689,8 @@ static int acpi_idle_play_dead(struct cpuidle_device *dev, int index)
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);
+ if (!kvm_para_available())
+ inl(acpi_gbl_FADT.xpm_timer_block.address);
} else
return -ENODEV;
}
--
MST
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH RFC] ACPI: disable extra P_LVLx access on KVM
2018-03-30 17:43 [PATCH RFC] ACPI: disable extra P_LVLx access on KVM Michael S. Tsirkin
@ 2018-04-23 8:07 ` Rafael J. Wysocki
2018-04-23 8:36 ` Paolo Bonzini
0 siblings, 1 reply; 3+ messages in thread
From: Rafael J. Wysocki @ 2018-04-23 8:07 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, Paolo Bonzini, Radim Krčmář,
kvm, Len Brown, linux-acpi
On Friday, March 30, 2018 7:43:58 PM CEST Michael S. Tsirkin wrote:
> As documented by commit b488f021 "ACPI: restore comment justifying
> 'extra' P_LVLx access", Linux does an extra IO read after entering idle
> because on (some) chipsets STPCLK# doesn't get asserted in time
> to prevent further instruction processing.
>
> This can never be the case on KVM, and a timer read causes an expensive
> VM exit in turn causing useless load on host system. Detect KVM and skip
> the read. TODO: whitelist more hypervisors?
>
> Note: very lightly tested. Pls don't apply this yet, I am working on a
> _CST implementation for KVM and will repost this without the RFC tag
> when it's been tested properly.
>
> Posting now for early flames/feedback.
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: kvm@vger.kernel.org
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> drivers/acpi/processor_idle.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index abb559c..8ae28dc 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -33,6 +33,7 @@
> #include <linux/cpuidle.h>
> #include <linux/cpu.h>
> #include <acpi/processor.h>
> +#include <linux/kvm_para.h>
>
> /*
> * Include the apic definitions for x86 to have the APIC timer related defines
> @@ -665,7 +666,8 @@ static void __cpuidle acpi_idle_do_entry(struct acpi_processor_cx *cx)
> /* 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);
> + if (!kvm_para_available())
> + inl(acpi_gbl_FADT.xpm_timer_block.address);
> }
> }
>
> @@ -687,7 +689,8 @@ static int acpi_idle_play_dead(struct cpuidle_device *dev, int index)
> 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);
> + if (!kvm_para_available())
> + inl(acpi_gbl_FADT.xpm_timer_block.address);
> } else
> return -ENODEV;
> }
>
While I have no objections to this change from the ACPI side, I'd like someone
from the KVM land to comment on this.
Thanks,
Rafael
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH RFC] ACPI: disable extra P_LVLx access on KVM
2018-04-23 8:07 ` Rafael J. Wysocki
@ 2018-04-23 8:36 ` Paolo Bonzini
0 siblings, 0 replies; 3+ messages in thread
From: Paolo Bonzini @ 2018-04-23 8:36 UTC (permalink / raw)
To: Rafael J. Wysocki, Michael S. Tsirkin
Cc: linux-kernel, Radim Krčmář, kvm, Len Brown, linux-acpi
On 23/04/2018 10:07, Rafael J. Wysocki wrote:
> On Friday, March 30, 2018 7:43:58 PM CEST Michael S. Tsirkin wrote:
>> As documented by commit b488f021 "ACPI: restore comment justifying
>> 'extra' P_LVLx access", Linux does an extra IO read after entering idle
>> because on (some) chipsets STPCLK# doesn't get asserted in time
>> to prevent further instruction processing.
>>
>> This can never be the case on KVM, and a timer read causes an expensive
>> VM exit in turn causing useless load on host system. Detect KVM and skip
>> the read. TODO: whitelist more hypervisors?
>>
>> Note: very lightly tested. Pls don't apply this yet, I am working on a
>> _CST implementation for KVM and will repost this without the RFC tag
>> when it's been tested properly.
>>
>> Posting now for early flames/feedback.
>>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>> Cc: kvm@vger.kernel.org
>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>> ---
>> drivers/acpi/processor_idle.c | 7 +++++--
>> 1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
>> index abb559c..8ae28dc 100644
>> --- a/drivers/acpi/processor_idle.c
>> +++ b/drivers/acpi/processor_idle.c
>> @@ -33,6 +33,7 @@
>> #include <linux/cpuidle.h>
>> #include <linux/cpu.h>
>> #include <acpi/processor.h>
>> +#include <linux/kvm_para.h>
>>
>> /*
>> * Include the apic definitions for x86 to have the APIC timer related defines
>> @@ -665,7 +666,8 @@ static void __cpuidle acpi_idle_do_entry(struct acpi_processor_cx *cx)
>> /* 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);
>> + if (!kvm_para_available())
>> + inl(acpi_gbl_FADT.xpm_timer_block.address);
>> }
>> }
>>
>> @@ -687,7 +689,8 @@ static int acpi_idle_play_dead(struct cpuidle_device *dev, int index)
>> 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);
>> + if (!kvm_para_available())
>> + inl(acpi_gbl_FADT.xpm_timer_block.address);
>> } else
>> return -ENODEV;
>> }
>>
>
> While I have no objections to this change from the ACPI side, I'd like someone
> from the KVM land to comment on this.
It would be nicer to blacklist the problematic chipsets, or as Michael
said have a way to whitelist more hypervisors, but this is certainly
okay from KVM land too.
Thanks,
paolo
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2018-04-23 8:36 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2018-03-30 17:43 [PATCH RFC] ACPI: disable extra P_LVLx access on KVM Michael S. Tsirkin
2018-04-23 8:07 ` Rafael J. Wysocki
2018-04-23 8:36 ` Paolo Bonzini
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