linux-kernel - [PATCH] perf: Add irq and exception return branch types

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Message-Id: <1645681014-3346-1-git-send-email-anshuman.khandual@arm.com>
Date:   Thu, 24 Feb 2022 11:06:54 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org
Subject: [PATCH] perf: Add irq and exception return branch types

This expands generic branch type classification by adding two more entries
there in i.e irq and exception return. Also updates the x86 implementation
to process X86_BR_IRET and X86_BR_IRQ records as appropriate. This changes
branch types reported to user space on x86 platform but it should not be a
problem. The possible scenarios and impacts are enumerated here.

--------------------------------------------------------------------------
| kernel | perf tool |                     Impact                        |
--------------------------------------------------------------------------
|   old  |    old    |  Works as before                                  |
--------------------------------------------------------------------------
|   old  |    new    |  PERF_BR_UNKNOWN is processed                     |
--------------------------------------------------------------------------
|   new  |    old    |  PERF_BR_ERET/IRQ are blocked via old PERF_BR_MAX |
--------------------------------------------------------------------------
|   new  |    new    |  PERF_BR_ERET/IRQ are recognized                  |
--------------------------------------------------------------------------

When PERF_BR_ERET/IRQ are blocked via old PERF_BR_MAX (new kernel with old
perf tool) the user space might throw up an warning complaining about some
unrecognized branch types being reported, but it is expected. PERF_BR_ERET
and PERF_BR_IRQ branch types will be used for BRBE implementation on arm64
platform.

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Will Deacon <will@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-perf-users@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
This applies on v5.17-rc5

These two new branch types expands generic branch type classification but
still leaves another three entries in 'type' field for later. Please refer
a previous discussion [1] for some further context.

[1] https://lore.kernel.org/all/1643348653-24367-1-git-send-email-anshuman.khandual@arm.com/

 arch/x86/events/intel/lbr.c           | 4 ++--
 include/uapi/linux/perf_event.h       | 2 ++
 tools/include/uapi/linux/perf_event.h | 2 ++
 tools/perf/util/branch.c              | 4 +++-
 4 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 669c2be14784..fe1742c4ca49 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -1329,10 +1329,10 @@ static int branch_map[X86_BR_TYPE_MAP_MAX] = {
 	PERF_BR_SYSCALL,	/* X86_BR_SYSCALL */
 	PERF_BR_SYSRET,		/* X86_BR_SYSRET */
 	PERF_BR_UNKNOWN,	/* X86_BR_INT */
-	PERF_BR_UNKNOWN,	/* X86_BR_IRET */
+	PERF_BR_ERET,		/* X86_BR_IRET */
 	PERF_BR_COND,		/* X86_BR_JCC */
 	PERF_BR_UNCOND,		/* X86_BR_JMP */
-	PERF_BR_UNKNOWN,	/* X86_BR_IRQ */
+	PERF_BR_IRQ,		/* X86_BR_IRQ */
 	PERF_BR_IND_CALL,	/* X86_BR_IND_CALL */
 	PERF_BR_UNKNOWN,	/* X86_BR_ABORT */
 	PERF_BR_UNKNOWN,	/* X86_BR_IN_TX */
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 82858b697c05..d37629dbad72 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -251,6 +251,8 @@ enum {
 	PERF_BR_SYSRET		= 8,	/* syscall return */
 	PERF_BR_COND_CALL	= 9,	/* conditional function call */
 	PERF_BR_COND_RET	= 10,	/* conditional function return */
+	PERF_BR_ERET		= 11,	/* exception return */
+	PERF_BR_IRQ		= 12,	/* irq */
 	PERF_BR_MAX,
 };
 
diff --git a/tools/include/uapi/linux/perf_event.h b/tools/include/uapi/linux/perf_event.h
index 82858b697c05..d37629dbad72 100644
--- a/tools/include/uapi/linux/perf_event.h
+++ b/tools/include/uapi/linux/perf_event.h
@@ -251,6 +251,8 @@ enum {
 	PERF_BR_SYSRET		= 8,	/* syscall return */
 	PERF_BR_COND_CALL	= 9,	/* conditional function call */
 	PERF_BR_COND_RET	= 10,	/* conditional function return */
+	PERF_BR_ERET		= 11,	/* exception return */
+	PERF_BR_IRQ		= 12,	/* irq */
 	PERF_BR_MAX,
 };
 
diff --git a/tools/perf/util/branch.c b/tools/perf/util/branch.c
index 2285b1eb3128..a9a909db8cc7 100644
--- a/tools/perf/util/branch.c
+++ b/tools/perf/util/branch.c
@@ -49,7 +49,9 @@ const char *branch_type_name(int type)
 		"SYSCALL",
 		"SYSRET",
 		"COND_CALL",
-		"COND_RET"
+		"COND_RET",
+		"ERET",
+		"IRQ"
 	};
 
 	if (type >= 0 && type < PERF_BR_MAX)
-- 
2.25.1