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Message-ID: <aDb6Mgg3TqyR2IRT@BLRRASHENOY1.amd.com>
Date: Wed, 28 May 2025 17:27:38 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: Manu Bretelle <chantr4@...il.com>
Cc: Mario Limonciello <mario.limonciello@....com>,
Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>,
"Rafael J . Wysocki" <rafael@...nel.org>,
Viresh Kumar <viresh.kumar@...aro.org>, linux-pm@...r.kernel.org,
linux-kernel@...r.kernel.org, Adam Clark <Adam.Clark@....com>
Subject: Re: [PATCH] acpi-cpufreq: Fix max-frequency computation
Hello Manu,
On Tue, May 27, 2025 at 08:24:27PM -0700, Manu Bretelle wrote:
> On Mon, Jan 13, 2025 at 10:11:07AM +0530, Gautham R. Shenoy wrote:
> > commit 3c55e94c0ade ("cpufreq: ACPI: Extend frequency tables to cover
> > boost frequencies") introduces an assumption in
> > acpi_cpufreq_cpu_init() that the first entry in the P-state table is
> > the nominal frequency. This assumption is incorrect. The frequency
> > corresponding to the P0 P-State need not be the same as the nominal
> > frequency advertised via CPPC.
> >
> > Since the driver is using the CPPC.highest_perf and CPPC.nominal_perf
> > to compute the boost-ratio, it makes sense to use CPPC.nominal_freq to
> > compute the max-frequency. CPPC.nominal_freq is advertised on
> > platforms supporting CPPC revisions 3 or higher.
> >
> > Hence, fallback to using the first entry in the P-State table only on
> > platforms that do not advertise CPPC.nominal_freq.
> >
>
> Gautham, this got recently pulled in 5.15.179 [0] but it seems to have broken
> what max CPU get reported.
Thanks for reporting this.
>
> I hit the issue on Ubuntu 22.04 with kernel 5.15.0-140-generic. My read from [1]
> is that that kernel is pretty much 5.15.79.
> I rebuilt it with this patch removed and max CPU now show as before.
>
> Here some output that may help, which is what is mostly down to what is reported
> by /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq . Posting the whole
> lscpu hoping that contain more useful data. Happy to provide more if needed.
>
> Ubuntu 22.04 with 5.15.0-140-generic (affected, note CPU max MHz: 2000.0000):
>
> $ lscpu
> Architecture: x86_64
> CPU op-mode(s): 32-bit, 64-bit
> Address sizes: 48 bits physical, 48 bits virtual
> Byte Order: Little Endian
> CPU(s): 128
> On-line CPU(s) list: 0-127
> Vendor ID: AuthenticAMD
> Model name: AMD EPYC 7713P 64-Core Processor
> CPU family: 25
> Model: 1
> Thread(s) per core: 2
> Core(s) per socket: 64
> Socket(s): 1
> Stepping: 1
> Frequency boost: enabled
> CPU max MHz: 2000.0000
> CPU min MHz: 1500.0000
[..snip..]
>
> With 5.15.0-999-generic (5.15.0-140-generic without this patch), max CPU is back
> to 3720.7029, which is also what I get with 5.15.0-139-generic.
>
> $ lscpu
> Architecture: x86_64
> CPU op-mode(s): 32-bit, 64-bit
> Address sizes: 48 bits physical, 48 bits virtual
> Byte Order: Little Endian
> CPU(s): 128
> On-line CPU(s) list: 0-127
> Vendor ID: AuthenticAMD
> Model name: AMD EPYC 7713P 64-Core Processor
> CPU family: 25
> Model: 1
> Thread(s) per core: 2
> Core(s) per socket: 64
> Socket(s): 1
> Stepping: 1
> Frequency boost: enabled
> CPU max MHz: 3720.7029
> CPU min MHz: 1500.0000
[..snip..]
>
>
> Thought to post here instead of [0] to get your thought on this. Am I missing
> something simple to get the right value? Or should this be pulled out of 5.15
> LTS?
No, the patch has a bug. The nominal_frequency returned from the
get_max_boost_ratio() function was in MHz, while cpufreq maintains
frequencies in KHz due to which the computed max_frequency was
incorrect and thus as a fallback, cpufreq reported P0 frequency as the
cpuinfo_max_freq.
Can you please try the following patch on top of the original one?
------------------------x8------------------------------------------------
>From 13d5c28823ed03353059801281d3b22e9f139a8d Mon Sep 17 00:00:00 2001
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
Date: Wed, 28 May 2025 16:43:33 +0530
Subject: [PATCH] acpi-cpufreq: Fix nominal_freq units to KHz in get_max_boost_ratio()
commit 083466754596 ("cpufreq: ACPI: Fix max-frequency computation")
modified get_max_boost_ratio() to return the nominal_freq advertised
in the _CPC object for the purposes of computing the maximum
frequency. The frequencies advertised in _CPC objects are in MHz but
cpufreq expects the frequency to be in KHz. Because the
nominal_frequency was not converted to KHz, the cpuinfo_max_frequency
that got computed was incorrect and the cpufreq reported the P0
frequency as the cpuinfo_max_freq.
Fix this by returning nominal_freq in KHz in get_max_boost_ratio()
Reported-by: Manu Bretelle <chantr4@...il.com>
Closes: https://lore.kernel.org/lkml/aDaB63tDvbdcV0cg@HQ-GR2X1W2P57/
Fixes: 083466754596 ("cpufreq: ACPI: Fix max-frequency computation")
Signed-off-by: Gautham R. Shenoy <gautham.shenoy@....com>
---
drivers/cpufreq/acpi-cpufreq.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index d26b610e4f24..76768fe213a9 100644
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -660,7 +660,7 @@ static u64 get_max_boost_ratio(unsigned int cpu, u64 *nominal_freq)
nominal_perf = perf_caps.nominal_perf;
if (nominal_freq)
- *nominal_freq = perf_caps.nominal_freq;
+ *nominal_freq = perf_caps.nominal_freq * 1000;
if (!highest_perf || !nominal_perf) {
pr_debug("CPU%d: highest or nominal performance missing\n", cpu);
--
2.34.1
--
Thanks and Regards
gautham.
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