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cpufreq(4) hwpstate: Yield CPU awaiting frequency change

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It doesn't seem necessary to busy the CPU while waiting to transition
into a different p-state.

PR:		221621 (related, but does not completely address)
Reviewed by:	truckman
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D12260
This commit is contained in:
Conrad Meyer 2017-09-07 20:20:12 +00:00
parent f9fc9faa3a
commit 2e81566368
1 changed files with 8 additions and 6 deletions
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8
sys/x86/cpufreq/hwpstate.c
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@ -160,6 +160,7 @@ DRIVER_MODULE(hwpstate, cpu, hwpstate_driver, hwpstate_devclass, 0, 0);
static int
hwpstate_goto_pstate(device_t dev, int pstate)
{
sbintime_t sbt;
int i;
uint64_t msr;
int j;
@ -197,10 +198,11 @@ hwpstate_goto_pstate(device_t dev, int pstate)
for (j = 0; j < 100; j++){
/* get the result. not assure msr=id */
msr = rdmsr(MSR_AMD_10H_11H_STATUS);
if(msr == id){
if (msr == id)
break;
}
DELAY(100);
sbt = SBT_1MS / 10;
tsleep_sbt(dev, PZERO, "pstate_goto", sbt,
sbt >> tc_precexp, 0);
}
HWPSTATE_DEBUG(dev, "result: P%d-state on cpu%d\n",
(int)msr, PCPU_GET(cpuid));