[tip: perf/core] perf/x86/amd/uncore: Use rdmsr if rdpmc is unavailable

[tip-bot2 for Sandipan Das]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     7ef0343855dc23a979a53b3143540f93f3e5bef8
Gitweb:        https://git.kernel.org/tip/7ef0343855dc23a979a53b3143540f93f3e5bef8
Author:        Sandipan Das <sandipan.das@xxxxxxx>
AuthorDate:    Thu, 05 Oct 2023 10:53:13 +05:30
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 09 Oct 2023 16:12:24 +02:00

perf/x86/amd/uncore: Use rdmsr if rdpmc is unavailable

Not all uncore PMUs may support the use of the RDPMC instruction for
reading counters. In such cases, read the count from the corresponding
PERF_CTR register using the RDMSR instruction.

Signed-off-by: Sandipan Das <sandipan.das@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/e9d994e32a3fcb39fa59fcf43ab4260d11aba097.1696425185.git.sandipan.das@xxxxxxx
---
 arch/x86/events/amd/uncore.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
index ff1d09c..2fe6239 100644
--- a/arch/x86/events/amd/uncore.c
+++ b/arch/x86/events/amd/uncore.c
@@ -96,7 +96,16 @@ static void amd_uncore_read(struct perf_event *event)
 	 */
 
 	prev = local64_read(&hwc->prev_count);
-	rdpmcl(hwc->event_base_rdpmc, new);
+
+	/*
+	 * Some uncore PMUs do not have RDPMC assignments. In such cases,
+	 * read counts directly from the corresponding PERF_CTR.
+	 */
+	if (hwc->event_base_rdpmc < 0)
+		rdmsrl(hwc->event_base, new);
+	else
+		rdpmcl(hwc->event_base_rdpmc, new);
+
 	local64_set(&hwc->prev_count, new);
 	delta = (new << COUNTER_SHIFT) - (prev << COUNTER_SHIFT);
 	delta >>= COUNTER_SHIFT;
@@ -164,6 +173,9 @@ out:
 	hwc->event_base_rdpmc = pmu->rdpmc_base + hwc->idx;
 	hwc->state = PERF_HES_UPTODATE | PERF_HES_STOPPED;
 
+	if (pmu->rdpmc_base < 0)
+		hwc->event_base_rdpmc = -1;
+
 	if (flags & PERF_EF_START)
 		event->pmu->start(event, PERF_EF_RELOAD);