tools/power/x86/intel-speed-select: Avoid current base freq as maximum

SST-PP level change results in online/offline of CPUs with -o option.
The Linux intel-pstate driver internally stores the current HWP_REQ MSR
value during offline and restores them during online.

It is possible that during SST-PP level change, the new HWP_CAP limits
can be updated. So, when a CPU is online, the HWP_REQ MSR should be
updated to new values based on HWP_CAP values.

This is particularly problematic when either turbo is disabled or the
current HWP_REQ value (stored before online) is less than the base
frequency from the updated HWP_CAP MSR guaranteed value. If the HWP_REQ
MSR is not updated, then the performance will be limited to the value
before perf level change.

Hence the tool updates cpufreq scaling_max_freq to the newer
base_frequency value in this case. This step is not required when HWP
interrupts are enabled, as the perf level change should result in a new
interrupt with HWP_GUARANTEED_PERF_CHANGE_STATUS and the intel_pstate
driver will update to new limits.

But the tool needs to handle the case when HWP interrupts are not
enabled but there is no way for the tool to know that HWP interrupts are
enabled or not. So, it has to still update the scaling_max_freq.

With the QOS changes in the kernel, user space writes to scaling_max_freq
are treated as hard limits. So, when base frequency is increased with
SST-BF enabled, the cpufreq subsystem will still not allow setting to the
SST-BF high priority core frequency. So, the HWP_REQ MSR will still be
capped to the user-set scaling_max_freq after SST-PP level change.

To address this, instead of setting scaling_max_freq to the current HWP_CAP
highest frequency, set it to the maximum integer value to set the QOS limit
as unconstrained. In this case, the actual HWP_REQ maximum frequency will
still be capped to HWP_CAP highest performance by the intel-pstate driver.
So, it will not result in invalid HWP_REQ values.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>

diff --git a/tools/power/x86/intel-speed-select/isst-config.c b/tools/power/x86/intel-speed-select/isst-config.c
index dd9056ddb016e9371e7877fb67b94d052c93b7b2..652ef1f567ad8f13e8d89f887d910c8d72cae6ba 100644 (file)
--- a/tools/power/x86/intel-speed-select/isst-config.c
+++ b/tools/power/x86/intel-speed-select/isst-config.c
@@ -1744,6 +1744,9 @@ static int no_turbo(void)
        return parse_int_file(0, "/sys/devices/system/cpu/intel_pstate/no_turbo");
 }
 
+#define U32_MAX                ((unsigned int)~0U)
+#define S32_MAX                ((int)(U32_MAX >> 1))
+
 static void adjust_scaling_max_from_base_freq(int cpu)
 {
        int base_freq, scaling_max_freq;
@@ -1751,7 +1754,7 @@ static void adjust_scaling_max_from_base_freq(int cpu)
        scaling_max_freq = parse_int_file(0, "/sys/devices/system/cpu/cpu%d/cpufreq/scaling_max_freq", cpu);
        base_freq = get_cpufreq_base_freq(cpu);
        if (scaling_max_freq < base_freq || no_turbo())
-               set_cpufreq_scaling_min_max(cpu, 1, base_freq);
+               set_cpufreq_scaling_min_max(cpu, 1, S32_MAX);
 }
 
 static void adjust_scaling_min_from_base_freq(int cpu)