[tip: x86/urgent] tools/power/turbostat: Fallback to an MSR read for EPB

[tip-bot2 for Borislav Petkov]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     7f1b11ba3564a391169420d98162987a12d0795d
Gitweb:        https://git.kernel.org/tip/7f1b11ba3564a391169420d98162987a12d0795d
Author:        Borislav Petkov <bp@xxxxxxx>
AuthorDate:    Thu, 28 Jan 2021 20:28:56 +01:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Wed, 03 Feb 2021 11:58:19 +01:00

tools/power/turbostat: Fallback to an MSR read for EPB

Commit

  6d6501d912a9 ("tools/power/turbostat: Read energy_perf_bias from sysfs")

converted turbostat to read the energy_perf_bias value from sysfs.
However, older kernels which do not have that file yet, would fail. For
those, fall back to the MSR reading.

Fixes: 6d6501d912a9 ("tools/power/turbostat: Read energy_perf_bias from sysfs")
Reported-by: Artem Bityutskiy <artem.bityutskiy@xxxxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Tested-by: Artem Bityutskiy <artem.bityutskiy@xxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210127132444.981120-1-dedekind1@xxxxxxxxx
---
 tools/power/x86/turbostat/turbostat.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
index 389ea52..a7c4f07 100644
--- a/tools/power/x86/turbostat/turbostat.c
+++ b/tools/power/x86/turbostat/turbostat.c
@@ -1834,12 +1834,15 @@ int get_mp(int cpu, struct msr_counter *mp, unsigned long long *counterp)
 int get_epb(int cpu)
 {
 	char path[128 + PATH_BYTES];
+	unsigned long long msr;
 	int ret, epb = -1;
 	FILE *fp;
 
 	sprintf(path, "/sys/devices/system/cpu/cpu%d/power/energy_perf_bias", cpu);
 
-	fp = fopen_or_die(path, "r");
+	fp = fopen(path, "r");
+	if (!fp)
+		goto msr_fallback;
 
 	ret = fscanf(fp, "%d", &epb);
 	if (ret != 1)
@@ -1848,6 +1851,11 @@ int get_epb(int cpu)
 	fclose(fp);
 
 	return epb;
+
+msr_fallback:
+	get_msr(cpu, MSR_IA32_ENERGY_PERF_BIAS, &msr);
+
+	return msr & 0xf;
 }
 
 void get_apic_id(struct thread_data *t)