Re: [PATCH] perf tools: allow overriding MAX_NR_CPUS at compile time

[Christophe LEROY <christophe.leroy@c-s.fr>]

Le 03/05/2018 à 15:40, Arnaldo Carvalho de Melo a écrit :
> Em Fri, Sep 22, 2017 at 01:20:43PM +0200, Christophe Leroy escreveu:
>> After update of kernel, perf tool doesn't run anymore on my
>> 32MB RAM powerpc board, but still runs on a 128MB RAM board:
> 
> Cleaning up my inbox, found this one, simple enough, still applies,
> applied.

Did you finally apply it ? I can't see it in linux-next. Will it be 
merged into 4.19 ?

Thanks
Christophe

> 
> These all needs to be dynamicly allocated, but still, with this one can
> get a functioning tool, apply it.
> 
> - Arnaldo
>   
>> ~# strace perf
>> execve("/usr/sbin/perf", ["perf"], [/* 12 vars */]) = -1 ENOMEM (Cannot allocate memory)
>> --- SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=0} ---
>> +++ killed by SIGSEGV +++
>> Segmentation fault
>>
>> objdump -x shows that .bss section has a huge size of 24Mbytes:
>>
>>   27 .bss          016baca8  101cebb8  101cebb8  001cd988  2**3
>>
>> With especially the following objects having quite big size
>>
>> 10205f80 l     O .bss	00140000              runtime_cycles_stats
>> 10345f80 l     O .bss	00140000              runtime_stalled_cycles_front_stats
>> 10485f80 l     O .bss	00140000              runtime_stalled_cycles_back_stats
>> 105c5f80 l     O .bss	00140000              runtime_branches_stats
>> 10705f80 l     O .bss	00140000              runtime_cacherefs_stats
>> 10845f80 l     O .bss	00140000              runtime_l1_dcache_stats
>> 10985f80 l     O .bss	00140000              runtime_l1_icache_stats
>> 10ac5f80 l     O .bss	00140000              runtime_ll_cache_stats
>> 10c05f80 l     O .bss	00140000              runtime_itlb_cache_stats
>> 10d45f80 l     O .bss	00140000              runtime_dtlb_cache_stats
>> 10e85f80 l     O .bss	00140000              runtime_cycles_in_tx_stats
>> 10fc5f80 l     O .bss	00140000              runtime_transaction_stats
>> 11105f80 l     O .bss	00140000              runtime_elision_stats
>> 11245f80 l     O .bss	00140000              runtime_topdown_total_slots
>> 11385f80 l     O .bss	00140000              runtime_topdown_slots_retired
>> 114c5f80 l     O .bss	00140000              runtime_topdown_slots_issued
>> 11605f80 l     O .bss	00140000              runtime_topdown_fetch_bubbles
>> 11745f80 l     O .bss	00140000              runtime_topdown_recovery_bubbles
>>
>> This is due to commit 4d255766d28b1 ("perf: Bump max number of cpus
>> to 1024"), because many tables are sized with MAX_NR_CPUS
>>
>> This patch gives the opportunity to redefine MAX_NR_CPUS via
>>
>> make EXTRA_CFLAGS=-DMAX_NR_CPUS=1
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
>> ---
>>   tools/perf/perf.h | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/tools/perf/perf.h b/tools/perf/perf.h
>> index dc442ba21bf6..a9db563da0a9 100644
>> --- a/tools/perf/perf.h
>> +++ b/tools/perf/perf.h
>> @@ -23,7 +23,9 @@ static inline unsigned long long rdclock(void)
>>   	return ts.tv_sec * 1000000000ULL + ts.tv_nsec;
>>   }
>>   
>> +#ifndef MAX_NR_CPUS
>>   #define MAX_NR_CPUS			1024
>> +#endif
>>   
>>   extern const char *input_name;
>>   extern bool perf_host, perf_guest;
>> -- 
>> 2.13.3