linux-kernel - [PATCH 1/3] perf/core: Change the layout of perf_sample

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Date:   Thu, 29 Dec 2022 12:40:59 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Ravi Bangoria <ravi.bangoria@....com>, bpf@...r.kernel.org
Subject: [PATCH 1/3] perf/core: Change the layout of perf_sample_data

The layout of perf_sample_data is designed to minimize cache-line
access.  The perf_sample_data_init() used to initialize a couple of
fields unconditionally so they were placed together at the head.

But it's changed now to set the fields according to the actual
sample_type flags.  The main user (the perf tools) sets the IP, TID,
TIME, PERIOD always.  Also group relevant fields like addr, phys_addr
and data_page_size.

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 include/linux/perf_event.h | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index c6a3bac76966..dd565306f479 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1098,47 +1098,51 @@ extern u64 perf_event_read_value(struct perf_event *event,
 
 struct perf_sample_data {
 	/*
-	 * Fields set by perf_sample_data_init(), group so as to
-	 * minimize the cachelines touched.
+	 * Fields set by perf_sample_data_init() unconditionally,
+	 * group so as to minimize the cachelines touched.
 	 */
 	u64				sample_flags;
 	u64				period;
 
 	/*
-	 * The other fields, optionally {set,used} by
-	 * perf_{prepare,output}_sample().
+	 * Fields commonly set by __perf_event_header__init_id(),
+	 * group so as to minimize the cachelines touched.
 	 */
-	struct perf_branch_stack	*br_stack;
-	union perf_sample_weight	weight;
-	union  perf_mem_data_src	data_src;
-	u64				txn;
-	u64				addr;
-	struct perf_raw_record		*raw;
-
 	u64				type;
-	u64				ip;
 	struct {
 		u32	pid;
 		u32	tid;
 	}				tid_entry;
 	u64				time;
 	u64				id;
-	u64				stream_id;
 	struct {
 		u32	cpu;
 		u32	reserved;
 	}				cpu_entry;
+
+	/*
+	 * The other fields, optionally {set,used} by
+	 * perf_{prepare,output}_sample().
+	 */
+	u64				ip;
 	struct perf_callchain_entry	*callchain;
-	u64				aux_size;
+	struct perf_raw_record		*raw;
+	struct perf_branch_stack	*br_stack;
+	union perf_sample_weight	weight;
+	union  perf_mem_data_src	data_src;
+	u64				txn;
 
 	struct perf_regs		regs_user;
 	struct perf_regs		regs_intr;
 	u64				stack_user_size;
 
-	u64				phys_addr;
+	u64				stream_id;
 	u64				cgroup;
+	u64				addr;
+	u64				phys_addr;
 	u64				data_page_size;
 	u64				code_page_size;
+	u64				aux_size;
 } ____cacheline_aligned;
 
 /* default value for data source */
-- 
2.39.0.314.g84b9a713c41-goog