RE: [PATCH 1/5] perf tools: Add fallback functions for cases where cpumode is insufficient

[Hunter, Adrian]

> -----Original Message-----
> From: Arnaldo Carvalho de Melo [mailto:acme@xxxxxxxxxx]
> Sent: Monday, November 5, 2018 9:36 PM
> To: Hunter, Adrian <adrian.hunter@xxxxxxxxx>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>; Andi Kleen <ak@xxxxxxxxxxxxxxx>; linux-
> kernel@xxxxxxxxxxxxxxx; leo.yan@xxxxxxxxxx; David Miller
> <davem@xxxxxxxxxxxxx>; Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Subject: Re: [PATCH 1/5] perf tools: Add fallback functions for cases where
> cpumode is insufficient
> 
> Em Mon, Nov 05, 2018 at 07:21:44PM +0000, Hunter, Adrian escreveu:
> > > In Monday, November 5, 2018 7:30 PM, Arnaldo Carvalho de Melo wrote
> <SNIP>
> > > > +struct map *thread__find_map_fallback(struct thread *thread, u8
> > > cpumode,
> > > > +				      u64 addr, struct addr_location *al) {
> 
> > > You named one as _fallback...
> 
> > > > +	struct map *map = thread__find_map(thread, cpumode, addr, al);
> > > > +	struct machine *machine = thread->mg->machine;
> > > > +	u8 addr_cpumode = machine__addr_cpumode(machine, cpumode,
> > > addr);
> > > > +
> > > > +	if (map || addr_cpumode == cpumode)
> > > > +		return map;
> > > > +
> > > > +	return thread__find_map(thread, addr_cpumode, addr, al); }
> > > > +
> > > >  struct symbol *thread__find_symbol(struct thread *thread, u8
> cpumode,
> > > >  				   u64 addr, struct addr_location *al)  { @@ -
> > > 1585,6 +1603,15 @@
> > > > struct symbol *thread__find_symbol(struct thread *thread, u8
> cpumode,
> > > >  	return al->sym;
> > > >  }
> 
> > > > +struct symbol *thread__find_symbol_fb(struct thread *thread, u8
> > > cpumode,
> > > > +				      u64 addr, struct addr_location *al)
> 
> > > ... and the other as _fb, make it consistent, please.
> 
> > ok
> 
> > > > +{
> > > > +	al->sym = NULL;
> > > > +	if (thread__find_map_fallback(thread, cpumode, addr, al))
> > > > +		al->sym = map__find_symbol(al->map, al->addr);
> > > > +	return al->sym;
> > > > +}
> 
> > > >  /*
> > > >   * Callers need to drop the reference to al->thread, obtained in
> > > >   * machine__findnew_thread()
> > > > diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> > > > index 111ae858cbcb..04edc0eac376 100644
> > > > --- a/tools/perf/util/machine.c
> > > > +++ b/tools/perf/util/machine.c
> > > > @@ -2542,6 +2542,46 @@ int machine__get_kernel_start(struct
> > > > machine
> > > *machine)
> > > >  	return err;
> > > >  }
> 
> > > > +/*
> > > > + * machine__single_ku_as - Machine has same address space for
> > > > +kernel
> > > and user.
> > > > + * @machine: machine object
> > > > + *
> > > > + * Some architectures have a single address space for kernel and
> > > > +user addresses,
> > > > + * which makes it possible to determine if an address is in
> > > > +kernel space or user
> > > > + * space.
> > > > + */
> > > > +static bool machine__single_ku_as(struct machine *machine) {
> > > > +	return strcmp(perf_env__arch(machine->env), "sparc"); }
> 
> > > Can we avoid having this strcmp be done repeatedly?
> 
> > It is only done if there are mapping errors
> 
> >  > Can we avoid having this strcmp be done repeatedly? I.e. just make
> > this a
> > > boolean initialized at session start, when machine->env is setup, so
> > > we'd
> > > have:
> 
> > >    machine->single_address_space
> 
> > > Instead of a function?
> 
> > Sure  thing.
> 
> Thanks
> 
> > >
> > > Also have you considered making this fallback to be performed only
> > > from code that is that arch specific?
> > >
> > > I.e. the code that supports branch samples/stacks is x86_86 specific
> > > at this point and thus only in that case we would call the routines
> > > that perform the fallback, which, in turn, wouldn't need to check for
> "sparc"?
> 
> > I will look at it, but theoretically someone could be processing x86
> > data but doing it on a machine of a different architecture.
> 
> Right, that should be supported, yes. What I meant was that when
> processing perf.data file with samples where the cpumode can't be inferred,
> we should use the fallback routines.
> 
> It is super unfortunate that we have addresses without a accompanying
> cpumode :-\ Don't you think those coulde be fixed somehow? If this comes
> from things synthesized from Intel PT traces, then we can use the address
> ranges for kernel/userspace to derive that before hitting the core code, that
> would be fed with addr/cpumode pairs, just like we have hdr.misc &
> USER/KERNEL and the PERF_CONTEXT_ markers in callchains.

Yes we will probably need to look at that, but at the moment I would like a fix for stable.