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hwpstate(4): Ignore CurPstateLimit by default

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Add a sysctl knob to allow users to re-enable it, and document the knob and
default in cpufreq.4.  (While here, add a few unrelated updates to
cpufreq.4.)

It seems that the register value in some hardware simply reflects the
configured P-state.  This results in an inadvertent and unintended outcome
where the P-state can only walk down, and then the driver becomes "stuck" in
the slowest possible P-state.

The Linux driver never consults this register, so that's some evidence that
ignoring the contents are relatively harmless.

PR:		234733
Reported by:	sigsys AT gmail.com, Erich Dollanksy <freebsd.ed.lists AT
		sumeritec.com>
This commit is contained in:
Conrad Meyer 2020-01-31 17:40:41 +00:00
parent a0dc3f8626
commit 43524989c5
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=357336
2 changed files with 37 additions and 12 deletions
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23
share/man/man4/cpufreq.4
View File

@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd January 22, 2020
.Dd January 31, 2020
.Dt CPUFREQ 4
.Os
.Sh NAME
@ -73,9 +73,13 @@ has passed (e.g., the system has cooled sufficiently).
If a sysctl cannot be set due to an override condition, it will return
.Er EPERM .
.Pp
The frequency cannot be changed if TSC is in use as the timecounter.
The frequency cannot be changed if TSC is in use as the timecounter and the
hardware does not support invariant TSC.
This is because the timecounter system needs to use a source that has a
constant rate.
(On invariant TSC hardware, the TSC runs at the P0 rate regardless of the
configured P-state.)
Modern hardware mostly has invariant TSC.
The timecounter source can be changed with the
.Pa kern.timecounter.hardware
sysctl.
@ -105,6 +109,15 @@ some systems.
.It Va debug.cpufreq.verbose
Print verbose messages.
This setting is also accessible via a tunable with the same name.
.It Va debug.hwpstate_pstate_limit
If enabled, the AMD hwpstate driver limits administrative control of P-states
(including by
.Xr powerd 8 )
to the value in the 0xc0010061 MSR, known as "PStateCurLim[CurPstateLimit]."
It is disabled (0) by default.
On some hardware, the limit register seems to simply follow the configured
P-state, which results in the inability to ever raise the P-state back to P0
from a reduced frequency state.
.El
.Sh SUPPORTED DRIVERS
The following device drivers offer absolute frequency control via the
@ -112,11 +125,15 @@ The following device drivers offer absolute frequency control via the
interface.
Usually, only one of these can be active at a time.
.Pp
.Bl -tag -compact -width ".Pa acpi_perf"
.Bl -tag -compact -width ".Pa hwpstate_intel"
.It Pa acpi_perf
ACPI CPU performance states
.It Pa est
Intel Enhanced SpeedStep
.It Pa hwpstate
AMD Cool'n'Quiet2 used in K10 through Family 17h
.It Pa hwpstate_intel
Intel SpeedShift driver
.It Pa ichss
Intel SpeedStep for ICH
.It Pa powernow

26
sys/x86/cpufreq/hwpstate_amd.c
View File

@ -131,6 +131,12 @@ static int hwpstate_verify;
SYSCTL_INT(_debug, OID_AUTO, hwpstate_verify, CTLFLAG_RWTUN,
&hwpstate_verify, 0, "Verify P-state after setting");
static bool hwpstate_pstate_limit;
SYSCTL_BOOL(_debug, OID_AUTO, hwpstate_pstate_limit, CTLFLAG_RWTUN,
&hwpstate_pstate_limit, 0,
"If enabled (1), limit administrative control of P-states to the value in "
"CurPstateLimit");
static device_method_t hwpstate_methods[] = {
/* Device interface */
DEVMETHOD(device_identify, hwpstate_identify),
@ -161,7 +167,8 @@ static driver_t hwpstate_driver = {
DRIVER_MODULE(hwpstate, cpu, hwpstate_driver, hwpstate_devclass, 0, 0);
/*
* Go to Px-state on all cpus considering the limit.
* Go to Px-state on all cpus, considering the limit register (if so
* configured).
*/
static int
hwpstate_goto_pstate(device_t dev, int id)
@ -170,14 +177,15 @@ hwpstate_goto_pstate(device_t dev, int id)
uint64_t msr;
int cpu, i, j, limit;
/* get the current pstate limit */
msr = rdmsr(MSR_AMD_10H_11H_LIMIT);
limit = AMD_10H_11H_GET_PSTATE_LIMIT(msr);
if (limit > id) {
HWPSTATE_DEBUG(dev,
"Restricting requested P%d to P%d due to HW limit\n", id,
limit);
id = limit;
if (hwpstate_pstate_limit) {
/* get the current pstate limit */
msr = rdmsr(MSR_AMD_10H_11H_LIMIT);
limit = AMD_10H_11H_GET_PSTATE_LIMIT(msr);
if (limit > id) {
HWPSTATE_DEBUG(dev, "Restricting requested P%d to P%d "
"due to HW limit\n", id, limit);
id = limit;
}
}
cpu = curcpu;