linux-kernel - Re: [PATCH] cpufreq: acpi: Defer setting boost MSRs

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Date:   Sun, 4 Dec 2022 13:20:34 -0600
From:   stuart hayes <stuart.w.hayes@...il.com>
To:     Borislav Petkov <bp@...en8.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Kyle Meyer <kyle.meyer@....com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: acpi: Defer setting boost MSRs



On 12/4/2022 12:29 PM, Borislav Petkov wrote:
> On Thu, Nov 03, 2022 at 07:19:47PM +0100, Rafael J. Wysocki wrote:
>> On Wed, Nov 2, 2022 at 9:01 PM Stuart Hayes <stuart.w.hayes@...il.com> wrote:
>>>
>>> When acpi-cpufreq is loaded, boost is enabled on every CPU (by setting an
>>> MSR) before the driver is registered with cpufreq.  This can be very time
>>> consuming, because it is done with a CPU hotplug startup callback, and
>>> cpuhp_setup_state() schedules the callback (cpufreq_boost_online()) to run
>>> on each CPU one at a time, waiting for each to run before calling the next.
>>>
>>> If cpufreq_register_driver() fails--if, for example, there are no ACPI
>>> P-states present--this is wasted time.
>>>
>>> Since cpufreq already sets up a CPU hotplug startup callback if and when
>>> acpi-cpufreq is registered, set the boost MSRs in acpi_cpufreq_cpu_init(),
>>> which is called by the cpufreq cpuhp callback.  This allows acpi-cpufreq to
>>> exit quickly if it is loaded but not needed.
>>>
>>> On one system with 192 CPUs, this patch speeds up boot by about 30 seconds.
>>>
>>> Signed-off-by: Stuart Hayes <stuart.w.hayes@...il.com>
>>> ---
>>>   drivers/cpufreq/acpi-cpufreq.c | 31 +++----------------------------
>>>   1 file changed, 3 insertions(+), 28 deletions(-)
> 
> ...
> 
>> Applied as 6.2 material, thanks!
> 
> My 32-bit Atom doesn't like this one. Reverting fixes it ofc.
> 
> [   22.780260] unchecked MSR access error: WRMSR to 0x1a0 (tried to write 0x0000004364950488) at rIP: 0xf80b37d4 (boost_set_msr.isra.0+0x9c/0x114 [acpi_cpufreq])
> [   22.781186] Call Trace:
> [   22.781186]  boost_set_msr_each+0x15/0x1c [acpi_cpufreq]
> [   22.781186]  __flush_smp_call_function_queue+0x132/0x1cc
> [   22.781186]  ? sysvec_call_function+0x30/0x30
> [   22.781186]  generic_smp_call_function_single_interrupt+0x12/0x18
> [   22.781186]  __sysvec_call_function_single.constprop.0+0x43/0x1d8
> [   22.781186]  sysvec_call_function_single+0x18/0x30
> [   22.781186]  handle_exception+0x133/0x133
> [   22.781186] EIP: finish_task_switch.isra.0+0x124/0x3a8
> [   22.781186] Code: d8 e8 8c 16 92 00 85 f6 75 e8 a1 04 24 6c c2 85 c0 0f 8f 9b 00 00 00 89 d8 e8 e4 02 92 00 e8 53 9e 0b 00 fb 64 a1 40 f9 69 c2 <8b> 80 5c 0f 00 00 85 c0 0f 85 72 01 00 00 a1 28 24 6c c2 64 8b 15
> [   22.781186] EAX: c32e2700 EBX: f748af40 ECX: 00000000 EDX: c1c3876e
> [   22.781186] ESI: 00000000 EDI: 00000000 EBP: c3241f90 ESP: c3241f78
> [   22.781186] DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 EFLAGS: 00000206
> [   22.781186]  ? uevent_seqnum_show+0x1b/0x28
> [   22.781186]  ? pid_list_refill_irq+0x128/0x1c0
> [   22.781186]  ? sysvec_call_function+0x30/0x30
> [   22.781186]  ? pid_list_refill_irq+0x128/0x1c0
> [   22.781186]  ? sysvec_call_function+0x30/0x30
> [   22.781186]  ? finish_task_switch.isra.0+0x124/0x3a8
> [   22.781186]  schedule_tail+0x12/0x78
> [   22.781186]  schedule_tail_wrapper+0x9/0x10
> [   22.781186]  ret_from_fork+0x5/0x28
> [   22.781186] EIP: 0xb7fba549
> [   22.781186] Code: Unable to access opcode bytes at 0xb7fba51f.
> [   22.781186] EAX: 00000000 EBX: 01200011 ECX: 00000000 EDX: 00000000
> [   22.781186] ESI: 00000000 EDI: b7bfe868 EBP: 00000000 ESP: bfcfedc0
> [   22.781186] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b EFLAGS: 00000246
> 

I believe I see the problem... acpi_cpufreq_cpu_init is calling set_boost() directly without checking to see if acpi_cpufreq_driver.set_boost was set, so it is trying to set the MSR on CPUs that don't support it.

Thanks, I can submit a patch to fix this.