RE: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline
[Public] > -Original Message- > From: Jan Beulich > Sent: Tuesday, May 20, 2025 5:16 PM > To: Penny, Zheng > Cc: Huang, Ray ; Andrew Cooper > ; Anthony PERARD ; > Orzel, Michal ; Julien Grall ; Roger Pau > Monné ; Stefano Stabellini ; > xen- > de...@lists.xenproject.org > Subject: Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen > cmdline > > On 20.05.2025 10:28, Penny, Zheng wrote: > > [Public] > > > >> -Original Message- > >> From: Jan Beulich > >> Sent: Monday, May 19, 2025 9:19 PM > >> To: Penny, Zheng > >> Cc: Huang, Ray ; Andrew Cooper > >> ; Anthony PERARD > >> ; Orzel, Michal ; > >> Julien Grall ; Roger Pau Monné > >> ; Stefano Stabellini ; > >> xen- de...@lists.xenproject.org > >> Subject: Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" > >> xen cmdline > >> > >> On 19.05.2025 10:36, Penny, Zheng wrote: > >>> [Public] > >>> > >>>> -Original Message- > >>>> From: Jan Beulich > >>>> Sent: Tuesday, April 29, 2025 8:52 PM > >>>> To: Penny, Zheng > >>>> Cc: Huang, Ray ; Andrew Cooper > >>>> ; Anthony PERARD > >>>> ; Orzel, Michal ; > >>>> Julien Grall ; Roger Pau Monné > >>>> ; Stefano Stabellini > >>>> ; > >>>> xen- de...@lists.xenproject.org > >>>> Subject: Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" > >>>> xen cmdline > >>>> > >>>> On 14.04.2025 09:40, Penny Zheng wrote: > >>>>> --- a/xen/include/acpi/cpufreq/processor_perf.h > >>>>> +++ b/xen/include/acpi/cpufreq/processor_perf.h > >>>>> @@ -5,6 +5,9 @@ > >>>>> #include > >>>>> #include > >>>>> > >>>>> +/* ability bits */ > >>>>> +#define XEN_PROCESSOR_PM_CPPC 8 > >>>> > >>>> This needs correlating (at least via commentary, better by > >>>> build-time > >>>> checking) with the other XEN_PROCESSOR_PM_* values. Otherwise > >> someone > >>>> adding a new #define in the public header may not (easily) notice a > >>>> possible conflict. With that in mind I also question whether 8 is > >>>> actually a good choice: That's the obvious next value to use in the > >>>> public interface. SIF_PM_MASK is 8 bits wide, so a sensible value > >>>> to use here > >> would by e.g. 0x100. > >>>> > >>> > >>> I've added a public flag anchor "XEN_PROCESSOR_PM_PUBLIC_END" in > >> public header: > >>> #define XEN_PROCESSOR_PM_PUBLIC_END > >> XEN_PROCESSOR_PM_TX > >>> and will do the following build-time checking: > >>> BUILD_BUG_ON(XEN_PROCESSOR_PM_CPPC <= > >>> XEN_PROCESSOR_PM_PUBLIC_END); > >> > >> I don't really see why anything would need to be added to the public > >> header (and we really should strive to avoid unnecessary additions). > > > > If I put such definition > > "#define XEN_PROCESSOR_PM_PUBLIC_END XEN_PROCESSOR_PM_TX" > > in internal header, I'm afraid it won't be updated if new ones added in the > > public in > the future. > > Or any other suggestions to provide build-time checking? > > Imo it's sufficient to check that the new #define doesn't overlap with > SIF_PM_MASK. Understood! > > Jan
Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline
On 20.05.2025 10:28, Penny, Zheng wrote: > [Public] > >> -Original Message- >> From: Jan Beulich >> Sent: Monday, May 19, 2025 9:19 PM >> To: Penny, Zheng >> Cc: Huang, Ray ; Andrew Cooper >> ; Anthony PERARD ; >> Orzel, Michal ; Julien Grall ; Roger >> Pau >> Monné ; Stefano Stabellini ; >> xen- >> de...@lists.xenproject.org >> Subject: Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen >> cmdline >> >> On 19.05.2025 10:36, Penny, Zheng wrote: >>> [Public] >>> >>>> -Original Message- >>>> From: Jan Beulich >>>> Sent: Tuesday, April 29, 2025 8:52 PM >>>> To: Penny, Zheng >>>> Cc: Huang, Ray ; Andrew Cooper >>>> ; Anthony PERARD >>>> ; Orzel, Michal ; >>>> Julien Grall ; Roger Pau Monné >>>> ; Stefano Stabellini ; >>>> xen- de...@lists.xenproject.org >>>> Subject: Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" >>>> xen cmdline >>>> >>>> On 14.04.2025 09:40, Penny Zheng wrote: >>>>> --- a/xen/include/acpi/cpufreq/processor_perf.h >>>>> +++ b/xen/include/acpi/cpufreq/processor_perf.h >>>>> @@ -5,6 +5,9 @@ >>>>> #include >>>>> #include >>>>> >>>>> +/* ability bits */ >>>>> +#define XEN_PROCESSOR_PM_CPPC 8 >>>> >>>> This needs correlating (at least via commentary, better by build-time >>>> checking) with the other XEN_PROCESSOR_PM_* values. Otherwise >> someone >>>> adding a new #define in the public header may not (easily) notice a >>>> possible conflict. With that in mind I also question whether 8 is >>>> actually a good choice: That's the obvious next value to use in the >>>> public interface. SIF_PM_MASK is 8 bits wide, so a sensible value to use >>>> here >> would by e.g. 0x100. >>>> >>> >>> I've added a public flag anchor "XEN_PROCESSOR_PM_PUBLIC_END" in >> public header: >>> #define XEN_PROCESSOR_PM_PUBLIC_END >> XEN_PROCESSOR_PM_TX >>> and will do the following build-time checking: >>> BUILD_BUG_ON(XEN_PROCESSOR_PM_CPPC <= >>> XEN_PROCESSOR_PM_PUBLIC_END); >> >> I don't really see why anything would need to be added to the public header >> (and we >> really should strive to avoid unnecessary additions). > > If I put such definition > "#define XEN_PROCESSOR_PM_PUBLIC_END XEN_PROCESSOR_PM_TX" > in internal header, I'm afraid it won't be updated if new ones added in the > public in the future. > Or any other suggestions to provide build-time checking? Imo it's sufficient to check that the new #define doesn't overlap with SIF_PM_MASK. Jan
RE: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline
[Public] > -Original Message- > From: Jan Beulich > Sent: Monday, May 19, 2025 9:19 PM > To: Penny, Zheng > Cc: Huang, Ray ; Andrew Cooper > ; Anthony PERARD ; > Orzel, Michal ; Julien Grall ; Roger Pau > Monné ; Stefano Stabellini ; > xen- > de...@lists.xenproject.org > Subject: Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen > cmdline > > On 19.05.2025 10:36, Penny, Zheng wrote: > > [Public] > > > >> -Original Message- > >> From: Jan Beulich > >> Sent: Tuesday, April 29, 2025 8:52 PM > >> To: Penny, Zheng > >> Cc: Huang, Ray ; Andrew Cooper > >> ; Anthony PERARD > >> ; Orzel, Michal ; > >> Julien Grall ; Roger Pau Monné > >> ; Stefano Stabellini ; > >> xen- de...@lists.xenproject.org > >> Subject: Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" > >> xen cmdline > >> > >> On 14.04.2025 09:40, Penny Zheng wrote: > >>> --- a/xen/include/acpi/cpufreq/processor_perf.h > >>> +++ b/xen/include/acpi/cpufreq/processor_perf.h > >>> @@ -5,6 +5,9 @@ > >>> #include > >>> #include > >>> > >>> +/* ability bits */ > >>> +#define XEN_PROCESSOR_PM_CPPC 8 > >> > >> This needs correlating (at least via commentary, better by build-time > >> checking) with the other XEN_PROCESSOR_PM_* values. Otherwise > someone > >> adding a new #define in the public header may not (easily) notice a > >> possible conflict. With that in mind I also question whether 8 is > >> actually a good choice: That's the obvious next value to use in the > >> public interface. SIF_PM_MASK is 8 bits wide, so a sensible value to use > >> here > would by e.g. 0x100. > >> > > > > I've added a public flag anchor "XEN_PROCESSOR_PM_PUBLIC_END" in > public header: > > #define XEN_PROCESSOR_PM_PUBLIC_END > XEN_PROCESSOR_PM_TX > > and will do the following build-time checking: > > BUILD_BUG_ON(XEN_PROCESSOR_PM_CPPC <= > > XEN_PROCESSOR_PM_PUBLIC_END); > > I don't really see why anything would need to be added to the public header > (and we > really should strive to avoid unnecessary additions). If I put such definition "#define XEN_PROCESSOR_PM_PUBLIC_END XEN_PROCESSOR_PM_TX" in internal header, I'm afraid it won't be updated if new ones added in the public in the future. Or any other suggestions to provide build-time checking? > > Jan
Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline
On 19.05.2025 10:36, Penny, Zheng wrote: > [Public] > >> -Original Message- >> From: Jan Beulich >> Sent: Tuesday, April 29, 2025 8:52 PM >> To: Penny, Zheng >> Cc: Huang, Ray ; Andrew Cooper >> ; Anthony PERARD ; >> Orzel, Michal ; Julien Grall ; Roger >> Pau >> Monné ; Stefano Stabellini ; >> xen- >> de...@lists.xenproject.org >> Subject: Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen >> cmdline >> >> On 14.04.2025 09:40, Penny Zheng wrote: >>> --- a/xen/include/acpi/cpufreq/processor_perf.h >>> +++ b/xen/include/acpi/cpufreq/processor_perf.h >>> @@ -5,6 +5,9 @@ >>> #include >>> #include >>> >>> +/* ability bits */ >>> +#define XEN_PROCESSOR_PM_CPPC 8 >> >> This needs correlating (at least via commentary, better by build-time >> checking) with >> the other XEN_PROCESSOR_PM_* values. Otherwise someone adding a new >> #define in the public header may not (easily) notice a possible conflict. >> With that in >> mind I also question whether 8 is actually a good choice: That's the obvious >> next >> value to use in the public interface. SIF_PM_MASK is 8 bits wide, so a >> sensible >> value to use here would by e.g. 0x100. >> > > I've added a public flag anchor "XEN_PROCESSOR_PM_PUBLIC_END" in public > header: > #define XEN_PROCESSOR_PM_PUBLIC_ENDXEN_PROCESSOR_PM_TX > and will do the following build-time checking: > BUILD_BUG_ON(XEN_PROCESSOR_PM_CPPC <= XEN_PROCESSOR_PM_PUBLIC_END); I don't really see why anything would need to be added to the public header (and we really should strive to avoid unnecessary additions). Jan
RE: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline
[Public] > -Original Message- > From: Jan Beulich > Sent: Tuesday, April 29, 2025 8:52 PM > To: Penny, Zheng > Cc: Huang, Ray ; Andrew Cooper > ; Anthony PERARD ; > Orzel, Michal ; Julien Grall ; Roger Pau > Monné ; Stefano Stabellini ; > xen- > de...@lists.xenproject.org > Subject: Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen > cmdline > > On 14.04.2025 09:40, Penny Zheng wrote: > > --- a/xen/include/acpi/cpufreq/processor_perf.h > > +++ b/xen/include/acpi/cpufreq/processor_perf.h > > @@ -5,6 +5,9 @@ > > #include > > #include > > > > +/* ability bits */ > > +#define XEN_PROCESSOR_PM_CPPC 8 > > This needs correlating (at least via commentary, better by build-time > checking) with > the other XEN_PROCESSOR_PM_* values. Otherwise someone adding a new > #define in the public header may not (easily) notice a possible conflict. > With that in > mind I also question whether 8 is actually a good choice: That's the obvious > next > value to use in the public interface. SIF_PM_MASK is 8 bits wide, so a > sensible > value to use here would by e.g. 0x100. > I've added a public flag anchor "XEN_PROCESSOR_PM_PUBLIC_END" in public header: #define XEN_PROCESSOR_PM_PUBLIC_ENDXEN_PROCESSOR_PM_TX and will do the following build-time checking: BUILD_BUG_ON(XEN_PROCESSOR_PM_CPPC <= XEN_PROCESSOR_PM_PUBLIC_END); > Jan
Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline
On 07.05.2025 07:27, Penny, Zheng wrote:
>> -Original Message-
>> From: Jan Beulich
>> Sent: Tuesday, April 29, 2025 8:52 PM
>>
>> On 14.04.2025 09:40, Penny Zheng wrote:
>>> @@ -573,6 +576,14 @@ ret_t do_platform_op(
>>> }
>>>
>>> case XEN_PM_CPPC:
>>> +if ( !(xen_processor_pmbits & XEN_PROCESSOR_PM_CPPC) )
>>> +{
>>> +ret = -EOPNOTSUPP;
>>> +break;
>>> +}
>>
>> While at least you no longer use -ENOSYS here, I question this behavior,
>> including
>> that for the pre-existing cases: How is the caller supposed to know whether
>> to
>> invoke this sub-op? Ignoring errors is generally not a good idea, so it
>> would be
>> better if the caller could blindly issue this request, getting back success
>> unless
>> there really was an issue with the data provided.
>>
>
> Understood.
> I will change it to ret = 0. Do you think we shall add warning info here?
No, for precisely ...
> Dom0 will send the CPPC data whenever it could.
... this reason.
Jan
> XEN_PROCESSOR_PM_CPPC
> is not set could largely be users choosing not to. In such case, silently
> getting back success
> shall be enough.
>
>
>> Jan
RE: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline
[Public]
Hi,
> -Original Message-
> From: Jan Beulich
> Sent: Tuesday, April 29, 2025 8:52 PM
> To: Penny, Zheng
> Cc: Huang, Ray ; Andrew Cooper
> ; Anthony PERARD ;
> Orzel, Michal ; Julien Grall ; Roger
> Pau Monné ; Stefano Stabellini ;
> xen-devel@lists.xenproject.org
> Subject: Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen
> cmdline
>
> On 14.04.2025 09:40, Penny Zheng wrote:
> > @@ -514,5 +515,16 @@ acpi_cpufreq_driver = {
> >
> > int __init acpi_cpufreq_register(void) {
> > -return cpufreq_register_driver(&acpi_cpufreq_driver);
> > +int ret;
> > +
> > +ret = cpufreq_register_driver(&acpi_cpufreq_driver);
> > +if ( ret )
> > +return ret;
> > +/*
> > + * After cpufreq driver registeration, XEN_PROCESSOR_PM_CPPC
> > + * and XEN_PROCESSOR_PM_PX shall become exclusive flags
> > + */
> > +xen_processor_pmbits &= ~XEN_PROCESSOR_PM_CPPC;
> > +
> > +return ret;
> > }
>
> Why is no similar adjustment needed in powernow_register_driver()? In
> principle I
> would have expected that it's not each individual driver which needs to care
> about
> this aspect, but that the framework is taking care of this.
>
Then maybe we shall add this here, to extract the codes from each specific
driver:
```
diff --git a/xen/arch/x86/acpi/cpufreq/cpufreq.c
b/xen/arch/x86/acpi/cpufreq/cpufreq.c
index eac1c125a3..9276241291 100644
--- a/xen/arch/x86/acpi/cpufreq/cpufreq.c
+++ b/xen/arch/x86/acpi/cpufreq/cpufreq.c
@@ -190,6 +190,25 @@ static int __init cf_check cpufreq_driver_init(void)
if ( ret != -ENODEV )
break;
}
+
+if ( !ret && i < cpufreq_xen_cnt )
+{
+switch ( cpufreq_xen_opts[i] )
+{
+case CPUFREQ_amd_cppc:
+xen_processor_pmbits &= ~XEN_PROCESSOR_PM_XEN;
+break;
+
+case CPUFREQ_xen:
+xen_processor_pmbits &= ~XEN_PROCESSOR_PM_CPPC;
+break;
+
+case CPUFREQ_none:
+default:
+break;
+}
+}
+
break;
}
}
```
> > @@ -573,6 +576,14 @@ ret_t do_platform_op(
> > }
> >
> > case XEN_PM_CPPC:
> > +if ( !(xen_processor_pmbits & XEN_PROCESSOR_PM_CPPC) )
> > +{
> > +ret = -EOPNOTSUPP;
> > +break;
> > +}
>
> While at least you no longer use -ENOSYS here, I question this behavior,
> including
> that for the pre-existing cases: How is the caller supposed to know whether to
> invoke this sub-op? Ignoring errors is generally not a good idea, so it would
> be
> better if the caller could blindly issue this request, getting back success
> unless
> there really was an issue with the data provided.
>
Understood.
I will change it to ret = 0. Do you think we shall add warning info here?
Dom0 will send the CPPC data whenever it could. XEN_PROCESSOR_PM_CPPC
is not set could largely be users choosing not to. In such case, silently
getting back success
shall be enough.
> Jan
Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline
On 14.04.2025 09:40, Penny Zheng wrote:
> @@ -514,5 +515,16 @@ acpi_cpufreq_driver = {
>
> int __init acpi_cpufreq_register(void)
> {
> -return cpufreq_register_driver(&acpi_cpufreq_driver);
> +int ret;
> +
> +ret = cpufreq_register_driver(&acpi_cpufreq_driver);
> +if ( ret )
> +return ret;
> +/*
> + * After cpufreq driver registeration, XEN_PROCESSOR_PM_CPPC
> + * and XEN_PROCESSOR_PM_PX shall become exclusive flags
> + */
> +xen_processor_pmbits &= ~XEN_PROCESSOR_PM_CPPC;
> +
> +return ret;
> }
Why is no similar adjustment needed in powernow_register_driver()? In principle
I would have expected that it's not each individual driver which needs to care
about this aspect, but that the framework is taking care of this.
> --- /dev/null
> +++ b/xen/arch/x86/acpi/cpufreq/amd-cppc.c
> @@ -0,0 +1,81 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * amd-cppc.c - AMD Processor CPPC Frequency Driver
> + *
> + * Copyright (C) 2025 Advanced Micro Devices, Inc. All Rights Reserved.
> + *
> + * Author: Penny Zheng
> + *
> + * AMD CPPC cpufreq driver introduces a new CPU performance scaling design
> + * for AMD processors using the ACPI Collaborative Performance and Power
> + * Control (CPPC) feature which provides finer grained frequency control
> range.
> + */
> +
> +#include
> +#include
> +#include
> +#include
> +
> +static bool __init amd_cppc_handle_option(const char *s, const char *end)
> +{
> +int ret;
> +
> +ret = parse_boolean("verbose", s, end);
> +if ( ret >= 0 )
> +{
> +cpufreq_verbose = ret;
> +return true;
> +}
> +
> +return false;
> +}
> +
> +int __init amd_cppc_cmdline_parse(const char *s, const char *e)
> +{
> +do
> +{
Nit (style): Brace placement is special here, just like it is ...
> +const char *end = strpbrk(s, ",;");
> +
> +if ( !amd_cppc_handle_option(s, end) )
> +{
> +printk(XENLOG_WARNING
> + "cpufreq/amd-cppc: option '%.*s' not recognized\n",
> + (int)((end ?: e) - s), s);
> +
> +return -EINVAL;
> +}
> +
> +s = end ? end + 1 : NULL;
> +} while ( s && s < e );
... here.
> --- a/xen/arch/x86/platform_hypercall.c
> +++ b/xen/arch/x86/platform_hypercall.c
> @@ -542,6 +542,9 @@ ret_t do_platform_op(
> ret = -ENOSYS;
> break;
> }
> +/* Xen doesn't support mixed mode */
> +ASSERT((xen_processor_pmbits & XEN_PROCESSOR_PM_CPPC) == 0);
Please prefer ! over "== 0" in such purely boolean contexts.
> @@ -573,6 +576,14 @@ ret_t do_platform_op(
> }
>
> case XEN_PM_CPPC:
> +if ( !(xen_processor_pmbits & XEN_PROCESSOR_PM_CPPC) )
> +{
> +ret = -EOPNOTSUPP;
> +break;
> +}
While at least you no longer use -ENOSYS here, I question this behavior,
including that for the pre-existing cases: How is the caller supposed to know
whether to invoke this sub-op? Ignoring errors is generally not a good idea,
so it would be better if the caller could blindly issue this request, getting
back success unless there really was an issue with the data provided.
> @@ -102,6 +103,9 @@ static int __init handle_cpufreq_cmdline(enum
> cpufreq_xen_opt option)
> cpufreq_xen_opts[cpufreq_xen_cnt++] = option;
> switch ( option )
> {
> +case CPUFREQ_amd_cppc:
> +xen_processor_pmbits |= XEN_PROCESSOR_PM_CPPC;
> +break;
> case CPUFREQ_hwp:
> case CPUFREQ_xen:
> xen_processor_pmbits |= XEN_PROCESSOR_PM_PX;
Here and (about) everywhere else: Blank line please between non-fall-through
case blocks. I guess I'm not going to repeat this any further. There are
very tiny switch() statements where it is okay to violate this principle, but
as a rule of thumb - if in doubt, put a blank line there.
> --- a/xen/include/acpi/cpufreq/processor_perf.h
> +++ b/xen/include/acpi/cpufreq/processor_perf.h
> @@ -5,6 +5,9 @@
> #include
> #include
>
> +/* ability bits */
> +#define XEN_PROCESSOR_PM_CPPC 8
This needs correlating (at least via commentary, better by build-time checking)
with the other XEN_PROCESSOR_PM_* values. Otherwise someone adding a new #define
in the public header may not (easily) notice a possible conflict. With that in
mind I also question whether 8 is actually a good choice: That's the obvious
next value to use in the public interface. SIF_PM_MASK is 8 bits wide, so a
sensible value to use here would by e.g. 0x100.
Jan
