linux-kernel - [PATCH 2/6] perf/x86/amd/uncore: Use rdmsr if rdpmc is unavailable

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Message-ID: <d48c60aea3a72c136811c0079f9802a988ee9271.1689748843.git.sandipan.das@amd.com>
Date:   Wed, 19 Jul 2023 12:25:37 +0530
From:   Sandipan Das <sandipan.das@....com>
To:     <linux-kernel@...r.kernel.org>, <linux-perf-users@...r.kernel.org>,
        <x86@...nel.org>
CC:     <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
        <mark.rutland@....com>, <alexander.shishkin@...ux.intel.com>,
        <jolsa@...nel.org>, <namhyung@...nel.org>, <irogers@...gle.com>,
        <adrian.hunter@...el.com>, <tglx@...utronix.de>, <bp@...en8.de>,
        <dave.hansen@...ux.intel.com>, <hpa@...or.com>,
        <eranian@...gle.com>, <ananth.narayan@....com>,
        <ravi.bangoria@....com>, <santosh.shukla@....com>,
        <sandipan.das@....com>
Subject: [PATCH 2/6] 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@....com>
---
 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 b0afbe6d9eb4..f17df6574ba5 100644
--- a/arch/x86/events/amd/uncore.c
+++ b/arch/x86/events/amd/uncore.c
@@ -76,7 +76,16 @@ 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;
@@ -144,6 +153,9 @@ static int amd_uncore_add(struct perf_event *event, int flags)
 	hwc->event_base_rdpmc = uncore->rdpmc_base + hwc->idx;
 	hwc->state = PERF_HES_UPTODATE | PERF_HES_STOPPED;
 
+	if (uncore->rdpmc_base < 0)
+		hwc->event_base_rdpmc = -1;
+
 	if (flags & PERF_EF_START)
 		event->pmu->start(event, PERF_EF_RELOAD);
 
-- 
2.34.1