linux-kernel - [PATCH v1 2/2] perf/x86: add cycles:pp alias for Intel Atom

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Date:	Wed,  2 Dec 2015 19:28:17 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	linux-kernel@...r.kernel.org
Cc:	acme@...hat.com, peterz@...radead.org, mingo@...e.hu,
	ak@...ux.intel.com, kan.liang@...el.com
Subject: [PATCH v1 2/2] perf/x86: add cycles:pp alias for Intel Atom

This patch updates the PEBS support for Intel Atom to provide
an alias for the cycles:pp event used by perf record/top by default
nowadays.

On Atom only INST_RETIRED:ANY supports PEBS, so we use this event
instead with a large cmask to count cycles.

Signed-off-by: Stephane Eranian <eranian@...gle.com>
---
 arch/x86/kernel/cpu/perf_event_intel.c    | 30 ++++++++++++++++++++++++++++++
 arch/x86/kernel/cpu/perf_event_intel_ds.c |  2 ++
 2 files changed, 32 insertions(+)

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 61f2577..7ff1e30 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -2475,6 +2475,35 @@ static void intel_pebs_aliases_snb(struct perf_event *event)
 	}
 }
 
+static void intel_pebs_aliases_atom(struct perf_event *event)
+{
+	if ((event->hw.config & X86_RAW_EVENT_MASK) == 0x003c) {
+		/*
+		 * Use an alternative encoding for CPU_CLK_UNHALTED.THREAD_P
+		 * (0x003c) so that we can use it with PEBS.
+		 *
+		 * The regular CPU_CLK_UNHALTED.THREAD_P event (0x003c) isn't
+		 * PEBS capable. However we can use UOPS_RETIRED.ALL
+		 * (0x01c2), which is a PEBS capable event, to get the same
+		 * count.
+		 *
+		 * INST_RETIRED.ANY counts the number of cycles that retires
+		 * CNTMASK instructions. By setting CNTMASK to a value (16)
+		 * larger than the maximum number of instructions that can be
+		 * retired per cycle (4) and then inverting the condition, we
+		 * count all cycles that retire 16 or less instructions, which
+		 * is every cycle.
+		 *
+		 * Thereby we gain a PEBS capable cycle counter.
+		 */
+		u64 alt_config = X86_CONFIG(.event=0xc0, .umask=0x00, .inv=1, .cmask=16);
+
+		alt_config |= (event->hw.config & ~X86_RAW_EVENT_MASK);
+		event->hw.config = alt_config;
+	}
+}
+
+
 static unsigned long intel_pmu_free_running_flags(struct perf_event *event)
 {
 	unsigned long flags = x86_pmu.free_running_flags;
@@ -3332,6 +3361,7 @@ __init int intel_pmu_init(void)
 
 		x86_pmu.event_constraints = intel_gen_event_constraints;
 		x86_pmu.pebs_constraints = intel_atom_pebs_event_constraints;
+		x86_pmu.pebs_aliases = intel_pebs_aliases_atom;
 		pr_cont("Atom events, ");
 		break;
 
diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c b/arch/x86/kernel/cpu/perf_event_intel_ds.c
index dae5f93..1b748ee 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_ds.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c
@@ -620,6 +620,8 @@ struct event_constraint intel_atom_pebs_event_constraints[] = {
 	INTEL_FLAGS_EVENT_CONSTRAINT(0xcb, 0x1),    /* MEM_LOAD_RETIRED.* */
 	/* INST_RETIRED.ANY_P, inv=1, cmask=16 (cycles:p). */
 	INTEL_FLAGS_EVENT_CONSTRAINT(0x108000c0, 0x01),
+	/* Allow all events as PEBS with no flags */
+	INTEL_ALL_EVENT_CONSTRAINT(0, 0x1),
 	EVENT_CONSTRAINT_END
 };
 
-- 
2.5.0

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