linux-kernel - [PATCH v2 03/10] perf/amd/ibs: Fix ->config to sample period calculation for OP pmu

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Message-ID: <20241206051713.991-4-ravi.bangoria@amd.com>
Date: Fri, 6 Dec 2024 05:17:06 +0000
From: Ravi Bangoria <ravi.bangoria@....com>
To: <peterz@...radead.org>, <mingo@...hat.com>, <namhyung@...nel.org>
CC: <ravi.bangoria@....com>, <acme@...nel.org>, <eranian@...gle.com>,
	<mark.rutland@....com>, <alexander.shishkin@...ux.intel.com>,
	<jolsa@...nel.org>, <irogers@...gle.com>, <adrian.hunter@...el.com>,
	<kan.liang@...ux.intel.com>, <tglx@...utronix.de>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
	<linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<santosh.shukla@....com>, <ananth.narayan@....com>, <sandipan.das@....com>
Subject: [PATCH v2 03/10] perf/amd/ibs: Fix ->config to sample period calculation for OP pmu

Instead of using standard perf_event_attr->freq=0 and ->sample_period
fields, IBS event in 'sample period mode' can also be opened by setting
period value directly in perf_event_attr->config in a MaxCnt bit-field
format.

IBS OP MaxCnt bits are defined as:

  (high bits) IbsOpCtl[26:20] = IbsOpMaxCnt[26:20]
  (low bits)  IbsOpCtl[15:0]  = IbsOpMaxCnt[19:4]

Perf event sample period can be derived from MaxCnt bits as:

  sample_period = (high bits) | ((low_bits) << 4);

However, current code just masks MaxCnt bits and shifts all of them,
including high bits, which is incorrect. Fix it.

Acked-by: Namhyung Kim <namhyung@...nel.org>
Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
---
 arch/x86/events/amd/ibs.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index 484606a9bf6b..63e1c1c11727 100644
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -268,7 +268,7 @@ static int perf_ibs_init(struct perf_event *event)
 {
 	struct hw_perf_event *hwc = &event->hw;
 	struct perf_ibs *perf_ibs;
-	u64 max_cnt, config;
+	u64 config;
 	int ret;
 
 	perf_ibs = get_ibs_pmu(event->attr.type);
@@ -300,10 +300,19 @@ static int perf_ibs_init(struct perf_event *event)
 		if (!hwc->sample_period)
 			hwc->sample_period = 0x10;
 	} else {
-		max_cnt = config & perf_ibs->cnt_mask;
+		u64 period = 0;
+
+		if (perf_ibs == &perf_ibs_op) {
+			period = (config & IBS_OP_MAX_CNT) << 4;
+			if (ibs_caps & IBS_CAPS_OPCNTEXT)
+				period |= config & IBS_OP_MAX_CNT_EXT_MASK;
+		} else {
+			period = (config & IBS_FETCH_MAX_CNT) << 4;
+		}
+
 		config &= ~perf_ibs->cnt_mask;
-		event->attr.sample_period = max_cnt << 4;
-		hwc->sample_period = event->attr.sample_period;
+		event->attr.sample_period = period;
+		hwc->sample_period = period;
 	}
 
 	if (!hwc->sample_period)
-- 
2.47.0