On 2025-03-26 10:54, Penny, Zheng wrote:
[Public]
Hi,
-----Original Message-----
From: Jan Beulich <jbeul...@suse.com>
Sent: Monday, March 24, 2025 11:48 PM
To: Penny, Zheng <penny.zh...@amd.com>
Cc: Huang, Ray <ray.hu...@amd.com>; Andrew Cooper
<andrew.coop...@citrix.com>; Roger Pau Monné <roger....@citrix.com>;
xen-
de...@lists.xenproject.org; Nicola Vetrini
<nicola.vetr...@bugseng.com>
Subject: Re: [PATCH v3 07/15] xen/cpufreq: fix core frequency
calculation for AMD
Family 1Ah CPUs
On 06.03.2025 09:39, Penny Zheng wrote:
> This commit fixes core frequency calculation for AMD Family 1Ah CPUs,
> due to a change in the PStateDef MSR layout in AMD Family 1Ah+.
> In AMD Family 1Ah+, Core current operating frequency in MHz is
> calculated as
> follows:
Why 1Ah+? In the code you correctly limit to just 1Ah.
> --- a/xen/arch/x86/cpu/amd.c
> +++ b/xen/arch/x86/cpu/amd.c
> @@ -572,12 +572,24 @@ static void amd_get_topology(struct cpuinfo_x86 *c)
> :
> c->cpu_core_id); }
>
> +static uint64_t amd_parse_freq(const struct cpuinfo_x86 *c, uint64_t
> +value) {
> + ASSERT(c->x86 <= 0x1A);
> +
> + if (c->x86 < 0x17)
> + return (((value & 0x3f) + 0x10) * 100) >> ((value >> 6) & 7);
> + else if (c->x86 <= 0x19)
> + return ((value & 0xff) * 25 * 8) / ((value >> 8) & 0x3f);
> + else
> + return (value & 0xfff) * 5;
> +}
Could I talk you into omitting the unnecessary "else" in cases like
this one?
(This may also make sense to express as switch().)
Sorry, bad habit... will change it to switch
> @@ -658,19 +670,20 @@ void amd_log_freq(const struct cpuinfo_x86 *c)
> if (!(lo >> 63))
> return;
>
> -#define FREQ(v) (c->x86 < 0x17 ? ((((v) & 0x3f) + 0x10) * 100) >> (((v) >> 6)
&
7) \
> - : (((v) & 0xff) * 25 * 8) / (((v) >> 8) &
0x3f))
> if (idx && idx < h &&
> !rdmsr_safe(0xC0010064 + idx, val) && (val >> 63) &&
> !rdmsr_safe(0xC0010064, hi) && (hi >> 63))
> printk("CPU%u: %lu (%lu ... %lu) MHz\n",
> - smp_processor_id(), FREQ(val), FREQ(lo), FREQ(hi));
> + smp_processor_id(),
> + amd_parse_freq(c, val),
> + amd_parse_freq(c, lo), amd_parse_freq(c, hi));
I fear Misra won't like multiple function calls to evaluate the
parameters to pass to
another function. Iirc smp_process_id() has special exception, so
that's okay here.
This may be possible to alleviate by marking the new helper pure or
even const
(see gcc doc as to caveats with passing pointers to const functions).
Cc-ing Nicola
for possible clarification or correction.
Maybe we shall declare the function __pure. Having checked the gcc doc,
``
a function that has pointer arguments must not be declared const
``
Otherwise we store the "c->x86" value to avoid using the pointer
Either way could work. ECLAIR will automatically pick up
__attribute__((pure)) or __attribute__((const)) from the declaration.
Maybe it could be const, as from a cursory look I don't think the gcc
restriction on pointer arguments applies, as the pointee is not modified
between successive calls, but I might be mistaken.
Jan
--
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253
