x86, sched: Account for CPUs with less than 4 cores in freq. invariance

If a CPU has less than 4 physical cores, MSR_TURBO_RATIO_LIMIT will
rightfully report that the 4C turbo ratio is zero. In such cases, use the
1C turbo ratio instead for frequency invariance calculations.

Fixes: 1567c3e3467c ("x86, sched: Add support for frequency invariance")
Reported-by: Like Xu <like.xu@linux.intel.com>
Reported-by: Neil Rickert <nwr10cst-oslnx@yahoo.com>
Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Link: https://lkml.kernel.org/r/20200416054745.740-3-ggherdovich@suse.cz

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 3a318ec..5d346b7 100644 (file)
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1945,18 +1945,23 @@ static bool skx_set_max_freq_ratio(u64 *base_freq, u64 *turbo_freq, int size)
 
 static bool core_set_max_freq_ratio(u64 *base_freq, u64 *turbo_freq)
 {
+       u64 msr;
        int err;
 
        err = rdmsrl_safe(MSR_PLATFORM_INFO, base_freq);
        if (err)
                return false;
 
-       err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT, turbo_freq);
+       err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT, &msr);
        if (err)
                return false;
 
-       *base_freq = (*base_freq >> 8) & 0xFF;      /* max P state */
-       *turbo_freq = (*turbo_freq >> 24) & 0xFF;   /* 4C turbo    */
+       *base_freq = (*base_freq >> 8) & 0xFF;    /* max P state */
+       *turbo_freq = (msr >> 24) & 0xFF;         /* 4C turbo    */
+
+       /* The CPU may have less than 4 cores */
+       if (!*turbo_freq)
+               *turbo_freq = msr & 0xFF;         /* 1C turbo    */
 
        return true;
 }