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

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Date:   Thu, 30 Nov 2017 16:05:25 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Cc:     Thomas Richter <tmricht@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        brueckner@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com
Subject: Re: [PATCH] perf annotate: Fix unnecessary memory allocation for
 s390x

Em Wed, Nov 29, 2017 at 06:04:56PM +0530, Ravi Bangoria escreveu:
> 
> 
> 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>

Thanks, applied.

- Arnaldo
 
> > 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;
> >  }
> >