diff mbox series

x86/cpu: Update power flags

Message ID 20231128-powerflags-v1-1-87e8fe020a3d@weissschuh.net
State New
Headers
Series x86/cpu: Update power flags |

Commit Message

Thomas Weißschuh Nov. 28, 2023, 6:54 p.m. UTC 
  As described on page 99 of
"Processing Programming Reference (PPR) for AMD Family 19h Model 61h, Revision B1 Processor".
(AMD Documentation Hub Document 56713)

Tested on an "AMD Ryzen 7 7840U w/ Radeon  780M Graphics".

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 arch/x86/kernel/cpu/powerflags.c | 3 +++
 1 file changed, 3 insertions(+)


---
base-commit: df60cee26a2e3d937a319229e335cb3f9c1f16d2
change-id: 20231128-powerflags-8ce66a96f6f3

Best regards,

Comments

Borislav Petkov Nov. 28, 2023, 7:12 p.m. UTC | #1 
On Tue, Nov 28, 2023 at 07:54:54PM +0100, Thomas Weißschuh wrote:
> As described on page 99 of
> "Processing Programming Reference (PPR) for AMD Family 19h Model 61h, Revision B1 Processor".
> (AMD Documentation Hub Document 56713)
> 
> Tested on an "AMD Ryzen 7 7840U w/ Radeon  780M Graphics".
> 
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
>  arch/x86/kernel/cpu/powerflags.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/powerflags.c b/arch/x86/kernel/cpu/powerflags.c
> index fd6ec2aa0303..0c98405aeae2 100644
> --- a/arch/x86/kernel/cpu/powerflags.c
> +++ b/arch/x86/kernel/cpu/powerflags.c
> @@ -21,4 +21,7 @@ const char *const x86_power_flags[32] = {
>  	"eff_freq_ro", /* Readonly aperf/mperf */
>  	"proc_feedback", /* processor feedback interface */
>  	"acc_power", /* accumulated power mechanism */
> +	"connected_standby", /* connected standby */
> +	"rapl", /* running average power limit */
> +	"fast_cppc", /* fast collaborative processor performance control */

No need.

The beginning of Documentation/arch/x86/cpuinfo.rst tries to explain
why.
Thomas Weißschuh Nov. 28, 2023, 7:25 p.m. UTC | #2 
On 2023-11-28 20:12:17+0100, Borislav Petkov wrote:
> On Tue, Nov 28, 2023 at 07:54:54PM +0100, Thomas Weißschuh wrote:
> > As described on page 99 of
> > "Processing Programming Reference (PPR) for AMD Family 19h Model 61h, Revision B1 Processor".
> > (AMD Documentation Hub Document 56713)
> > 
> > Tested on an "AMD Ryzen 7 7840U w/ Radeon  780M Graphics".
> > 
> > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> > ---
> >  arch/x86/kernel/cpu/powerflags.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/cpu/powerflags.c b/arch/x86/kernel/cpu/powerflags.c
> > index fd6ec2aa0303..0c98405aeae2 100644
> > --- a/arch/x86/kernel/cpu/powerflags.c
> > +++ b/arch/x86/kernel/cpu/powerflags.c
> > @@ -21,4 +21,7 @@ const char *const x86_power_flags[32] = {
> >  	"eff_freq_ro", /* Readonly aperf/mperf */
> >  	"proc_feedback", /* processor feedback interface */
> >  	"acc_power", /* accumulated power mechanism */
> > +	"connected_standby", /* connected standby */
> > +	"rapl", /* running average power limit */
> > +	"fast_cppc", /* fast collaborative processor performance control */
> 
> No need.
> 
> The beginning of Documentation/arch/x86/cpuinfo.rst tries to explain
> why.

Isn't this introduction more about the cpuinfo "flags" fields?
These power management flags have their own field "power management".

Without the patch it looks like this on my machine in cpuinfo:

  power management: ts ttp tm hwpstate cpb eff_freq_ro [13] [14] [15]

So they are already reported, but only their numeric value.

Anyways, if it's not correct to have them then let's drop the patch.


Thomas
Borislav Petkov Nov. 28, 2023, 7:36 p.m. UTC | #3 
On Tue, Nov 28, 2023 at 08:25:40PM +0100, Thomas Weißschuh wrote:
> > The beginning of Documentation/arch/x86/cpuinfo.rst tries to explain
> > why.
> 
> Isn't this introduction more about the cpuinfo "flags" fields?

That's why I said "tries to explain". See below - I've been meaning to
write this for a long time now.

>   power management: ts ttp tm hwpstate cpb eff_freq_ro [13] [14] [15]

Yeah, nothing cares about those - see below.

Thx.

---
diff --git a/Documentation/arch/x86/cpuinfo.rst b/Documentation/arch/x86/cpuinfo.rst
index 08246e8ac835..95c7ebcc13a9 100644
--- a/Documentation/arch/x86/cpuinfo.rst
+++ b/Documentation/arch/x86/cpuinfo.rst
@@ -13,6 +13,29 @@ or KVM want to expose the feature to a KVM guest, it can and should have
 an X86_FEATURE_* defined. These flags represent hardware features as
 well as software features.
 
+The /proc/cpuinfo list is not exhaustive and represents an ill-fated
+attempt from long time ago to put feature flags in an easy to find place
+for userspace. However,
+
+* the amount of feature flags is growing by the CPU generation, leading
+to unparseable and unwieldy /proc/cpuinfo
+
+* what is more, those feature flags even need to be in that file because
+userspace doesn't even care about them - glibc et al already use CPUID
+to find out what the target machine supports and what not. And even if
+it doesn't do that and the hw supports CPUID faulting, userspace can
+simply probe for the feature and figure out if it is supported or not
+
+* furthermore, those flag strings become an ABI the moment they appear
+there and maintaining them forever when nothing even uses them is a lot
+of wasted effort
+
+So, the current use of /proc/cpuinfo is to show features which the
+kernel has *enabled* and supports. As in: the CPUID feature flag is
+there, there's an additional setup which the kernel has done while
+booting and the functionality is there and ready to use. A perfect
+example for that is "user_shstk".
+
 If users want to know if a feature is available on a given system, they
 try to find the flag in /proc/cpuinfo. If a given flag is present, it
 means that the kernel supports it and is currently making it available.
diff mbox series

Patch

diff --git a/arch/x86/kernel/cpu/powerflags.c b/arch/x86/kernel/cpu/powerflags.c
index fd6ec2aa0303..0c98405aeae2 100644
--- a/arch/x86/kernel/cpu/powerflags.c
+++ b/arch/x86/kernel/cpu/powerflags.c
@@ -21,4 +21,7 @@  const char *const x86_power_flags[32] = {
 	"eff_freq_ro", /* Readonly aperf/mperf */
 	"proc_feedback", /* processor feedback interface */
 	"acc_power", /* accumulated power mechanism */
+	"connected_standby", /* connected standby */
+	"rapl", /* running average power limit */
+	"fast_cppc", /* fast collaborative processor performance control */
 };