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

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Message-Id: <a5f06775-0d93-d57d-809a-cb198578ebfc@linux.vnet.ibm.com>
Date:   Wed, 29 Nov 2017 18:04:56 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
To:     Thomas Richter <tmricht@...ux.vnet.ibm.com>, acme@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        brueckner@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: Re: [PATCH] perf annotate: Fix unnecessary memory allocation for
 s390x



On 11/24/2017 03:16 PM, Thomas Richter wrote:
> 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.

Ack-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>

> 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;
>  }
>