tools/power turbostat: Allow Zero return value for some RAPL registers

turbostat aborted with below messages on a dual-package system,

   turbostat: turbostat.c:3744: rapl_counter_accumulate: Assertion `dst->unit == src->unit' failed.
   Aborted

This is because
1. the MSR_DRAM_PERF_STATUS returns Zero for one package, and non-Zero
   for another package
2. probe_msr() treats Zero return value as a failure so this feature is
   enabled on one package, and disabled for another package.
3. turbostat aborts because the feature is invalid on some package

Unlike the RAPL energy counter registers, MSR_DRAM_PERF_STATUS can
return Zero value, and this should not be treated as a failure.

Fix the problem by allowing Zero return value for RAPL registers other
than the energy counters.

Fixes: 7c6fee2 ("tools/power turbostat: Check for non-zero value when MSR probing")
Reported-by: Artem Bityutskiy <[email protected]>
Signed-off-by: Zhang Rui <[email protected]>
Signed-off-by: Len Brown <[email protected]>

Author: zhang-rui

tools/power/x86/turbostat/turbostat.c

@@ -2211,7 +2211,7 @@ int get_msr(int cpu, off_t offset, unsigned long long *msr)
 	return 0;
 }
 
-int probe_msr(int cpu, off_t offset)
+int probe_rapl_msr(int cpu, off_t offset, int index)
 {
 	ssize_t retval;
 	unsigned long long value;
@@ -2220,13 +2220,22 @@ int probe_msr(int cpu, off_t offset)
 
 	retval = pread(get_msr_fd(cpu), &value, sizeof(value), offset);
 
-	/*
-	 * Expect MSRs to accumulate some non-zero value since the system was powered on.
-	 * Treat zero as a read failure.
-	 */
-	if (retval != sizeof(value) || value == 0)
+	/* if the read failed, the probe fails */
+	if (retval != sizeof(value))
 		return 1;
 
+	/* If an Energy Status Counter MSR returns 0, the probe fails */
+	switch (index) {
+	case RAPL_RCI_INDEX_ENERGY_PKG:
+	case RAPL_RCI_INDEX_ENERGY_CORES:
+	case RAPL_RCI_INDEX_DRAM:
+	case RAPL_RCI_INDEX_GFX:
+	case RAPL_RCI_INDEX_ENERGY_PLATFORM:
+		if (value == 0)
+			return 1;
+	}
+
+	/* PKG,DRAM_PERF_STATUS MSRs, can return any value */
 	return 0;
 }
 
@@ -7907,7 +7916,7 @@ void rapl_perf_init(void)
 					rci->flags[cai->rci_index] = cai->flags;
 
 					/* Use MSR for this counter */
-				} else if (!no_msr && cai->msr && probe_msr(cpu, cai->msr) == 0) {
+				} else if (!no_msr && cai->msr && probe_rapl_msr(cpu, cai->msr, cai->rci_index) == 0) {
 					rci->source[cai->rci_index] = COUNTER_SOURCE_MSR;
 					rci->msr[cai->rci_index] = cai->msr;
 					rci->msr_mask[cai->rci_index] = cai->msr_mask;
@@ -8045,7 +8054,7 @@ void msr_perf_init_(void)
 					cai->present = true;
 
 					/* User MSR for this counter */
-				} else if (!no_msr && cai->msr && probe_msr(cpu, cai->msr) == 0) {
+				} else if (!no_msr && cai->msr && probe_rapl_msr(cpu, cai->msr, cai->rci_index) == 0) {
 					cci->source[cai->rci_index] = COUNTER_SOURCE_MSR;
 					cci->msr[cai->rci_index] = cai->msr;
 					cci->msr_mask[cai->rci_index] = cai->msr_mask;
@@ -8159,7 +8168,7 @@ void cstate_perf_init_(bool soft_c1)
 
 					/* User MSR for this counter */
 				} else if (!no_msr && cai->msr && pkg_cstate_limit >= cai->pkg_cstate_limit
-					   && probe_msr(cpu, cai->msr) == 0) {
+					   && probe_rapl_msr(cpu, cai->msr, cai->rci_index) == 0) {
 					cci->source[cai->rci_index] = COUNTER_SOURCE_MSR;
 					cci->msr[cai->rci_index] = cai->msr;
 				}