Re: [PATCH][RFC v4] ACPI throttling: Disable the MSR T-state if enabled after resumed

From: Pavel Machek
Date: Sat Feb 18 2017 - 04:03:05 EST

On Fri 2017-02-17 16:27:30, Chen Yu wrote:
> Previously a bug was reported that on certain Broadwell
> platform, after resumed from S3, the CPU is running at
> an anomalously low speed, due to the BIOS has enabled the
> MSR throttling across S3. The solution to this was to introduce
> a quirk framework to save/restore tstate MSR register around
> suspend/resume, in Commit 7a9c2dd08ead ("x86/pm:
> Introduce quirk framework to save/restore extra MSR
> registers around suspend/resume").
> However there are still three problems left:
> 1. More and more reports show that other platforms also
> encountered the same issue, so the quirk list might
> be endless.
> 2. Each CPUs should take the save/restore operation into
> consideration, rather than the boot CPU alone.
> 3. Normally ACPI T-state re-evaluation is done on resume,
> however there is no _TSS on the bogus platform, thus
> above re-evaluation code does not run on that machine.
> Solution:
> This patch is based on the fact that, we generally should not
> expect the system to come back from resume with throttling
> enabled, but leverage the OS components to deal with it,
> such as thermal event. So we simply clear the MSR T-state
> and print the warning if it is found to be enabled after
> resumed back. Besides, we can remove the quirk in previous patch
> later.

What if the machine _is_ hot?

> +static int acpi_throttling_init_ops(void)
> +{
> + /*
> + * Reevaluate on boot CPU. Since it is not always CPU0,
> + * we can not invoke throttling_msr_reevaluate(0) directly.
> + */

Boot cpu is not cpu#0? How can that be?

Should we introduce generic framework to "fix" all the cpus? Actually,
should this be done right on cpu hotplug?

(cesky, pictures)

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