linux-kernel - [PATCH] perf annotate: Fix unnecessary memory allocation for s390x

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Date:   Fri, 24 Nov 2017 10:46:37 +0100
From:   Thomas Richter <tmricht@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        acme@...nel.org
Cc:     brueckner@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com,
        Thomas Richter <tmricht@...ux.vnet.ibm.com>
Subject: [PATCH] perf annotate: Fix unnecessary memory allocation for s390x

This patch fixes a bug introduced with commit d9f8dfa9baf9
("perf annotate s390: Implement jump types for perf annotate").

Perf annotate displays annotated assembler output by reading
output of command objdump and parsing the disassembled lines. For
each shown mnemonic this function sequence is executed:

  disasm_line__new()
  |
  +--> disasm_line__init_ins()
       |
       +--> ins__find()
            |
            +--> arch->associate_instruction_ops()

The s390x specific function assigned to function pointer
associate_instruction_ops refers to function
s390__associate_ins_ops(). This function checks for supported
mnemonics and assigns a NULL pointer to unsupported mnemonics.
However even the NULL pointer is added to the architecture
dependend instruction array.

This leads to an extremely large architecture instruction array
(due to array resize logic in function arch__grow_instructions()).
Depending on the objdump output being parsed the array can end up
with several ten-thousand elements.

This patch checks if a mnemonic is supported and only adds
supported ones into the architecture instruction array. The
array does not contain elements with NULL pointers anymore.

Before the patch (With some debug printf output):
[root@...lp76 perf]# time ./perf annotate --stdio > /tmp/xxxbb

real	8m49.679s
user	7m13.008s
sys	0m1.649s
[root@...lp76 perf]# fgrep '__ins__find sorted:1 nr_instructions:'
			/tmp/xxxbb | tail -1
__ins__find sorted:1 nr_instructions:87433 ins:0x341583c0
[root@...lp76 perf]#

The number of different s390x branch/jump/call/return instructions
entered into the array is 87433.

After the patch (With some printf debug output:)

[root@...lp76 perf]# time ./perf annotate --stdio > /tmp/xxxaa

real	1m24.553s
user	0m0.587s
sys	0m1.530s
[root@...lp76 perf]# fgrep '__ins__find sorted:1 nr_instructions:'
			/tmp/xxxaa | tail -1
__ins__find sorted:1 nr_instructions:56 ins:0x3f406570
[root@...lp76 perf]#

The number of different s390x branch/jump/call/return instructions
entered into the array is 56 which is sensible.

Signed-off-by: Thomas Richter <tmricht@...ux.vnet.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
---
 tools/perf/arch/s390/annotate/instructions.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/arch/s390/annotate/instructions.c b/tools/perf/arch/s390/annotate/instructions.c
index c9a81673e8aa..89f0b6c00e3f 100644
--- a/tools/perf/arch/s390/annotate/instructions.c
+++ b/tools/perf/arch/s390/annotate/instructions.c
@@ -16,7 +16,8 @@ static struct ins_ops *s390__associate_ins_ops(struct arch *arch, const char *na
 	if (!strcmp(name, "br"))
 		ops = &ret_ops;

-	arch__associate_ins_ops(arch, name, ops);
+	if (ops)
+		arch__associate_ins_ops(arch, name, ops);
 	return ops;
 }

-- 
2.13.4