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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Wed, Oct 31, 2018 at 11:10:39AM +0200, Adrian Hunter escreveu:
> For branch stacks or branch samples, the sample cpumode might not be
> correct because it applies only to the sample 'ip' and not necessary to
> 'addr' or branch stack addresses. Add fallback functions that can be used
> to deal with those cases
> 
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> Cc: stable@vger.kernel.org # 4.19
> ---
>  tools/perf/util/event.c   | 27 ++++++++++++++++++++++++++
>  tools/perf/util/machine.c | 40 +++++++++++++++++++++++++++++++++++++++
>  tools/perf/util/machine.h |  2 ++
>  tools/perf/util/thread.h  |  4 ++++
>  4 files changed, 73 insertions(+)
> 
> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
> index bc646185f8d9..52b24b8ce29e 100644
> --- a/tools/perf/util/event.c
> +++ b/tools/perf/util/event.c
> @@ -1576,6 +1576,24 @@ struct map *thread__find_map(struct thread *thread, u8 cpumode, u64 addr,
>  	return al->map;
>  }
>  
> +/*
> + * For branch stacks or branch samples, the sample cpumode might not be correct
> + * because it applies only to the sample 'ip' and not necessary to 'addr' or
> + * branch stack addresses. If possible, use a fallback to deal with those cases.
> + */
> +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.

> +{
> +	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? 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?

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"?

> +
> +u8 machine__addr_cpumode(struct machine *machine, u8 cpumode, u64 addr)
> +{
> +	u8 addr_cpumode = cpumode;
> +	bool kernel_ip;
> +
> +	if (!machine__single_ku_as(machine))
> +		goto out;
> +
> +	kernel_ip = machine__kernel_ip(machine, addr);
> +	switch (cpumode) {
> +	case PERF_RECORD_MISC_KERNEL:
> +	case PERF_RECORD_MISC_USER:
> +		addr_cpumode = kernel_ip ? PERF_RECORD_MISC_KERNEL :
> +					   PERF_RECORD_MISC_USER;
> +		break;
> +	case PERF_RECORD_MISC_GUEST_KERNEL:
> +	case PERF_RECORD_MISC_GUEST_USER:
> +		addr_cpumode = kernel_ip ? PERF_RECORD_MISC_GUEST_KERNEL :
> +					   PERF_RECORD_MISC_GUEST_USER;
> +		break;
> +	default:
> +		break;
> +	}
> +out:
> +	return addr_cpumode;
> +}
> +
>  struct dso *machine__findnew_dso(struct machine *machine, const char *filename)
>  {
>  	return dsos__findnew(&machine->dsos, filename);
> diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
> index d856b85862e2..20d464135ed1 100644
> --- a/tools/perf/util/machine.h
> +++ b/tools/perf/util/machine.h
> @@ -99,6 +99,8 @@ static inline bool machine__kernel_ip(struct machine *machine, u64 ip)
>  	return ip >= kernel_start;
>  }
>  
> +u8 machine__addr_cpumode(struct machine *machine, u8 cpumode, u64 addr);
> +
>  struct thread *machine__find_thread(struct machine *machine, pid_t pid,
>  				    pid_t tid);
>  struct comm *machine__thread_exec_comm(struct machine *machine,
> diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
> index 36c09a9904e6..e28f9dc1110a 100644
> --- a/tools/perf/util/thread.h
> +++ b/tools/perf/util/thread.h
> @@ -96,9 +96,13 @@ struct thread *thread__main_thread(struct machine *machine, struct thread *threa
>  
>  struct map *thread__find_map(struct thread *thread, u8 cpumode, u64 addr,
>  			     struct addr_location *al);
> +struct map *thread__find_map_fallback(struct thread *thread, u8 cpumode,
> +				      u64 addr, struct addr_location *al);
>  
>  struct symbol *thread__find_symbol(struct thread *thread, u8 cpumode,
>  				   u64 addr, struct addr_location *al);
> +struct symbol *thread__find_symbol_fb(struct thread *thread, u8 cpumode,
> +				      u64 addr, struct addr_location *al);
>  
>  void thread__find_cpumode_addr_location(struct thread *thread, u64 addr,
>  					struct addr_location *al);
> -- 
> 2.17.1