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

[Christophe LEROY]

Le 03/05/2018 Ã 15:40, Arnaldo Carvalho de Melo a ÃcritÂ:
> 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@xxxxxx>
> > ---
> >   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