Subject: [RFC 1/3] perf tool: Introduce arch-specific supplemental perf open strerror capability

From: [email-masked] (Arnaldo Carvalho de Melo)
Date: Tue, 24 Oct 2017 12:27:44 -0200

Em Tue, Oct 24, 2017 at 03:04:04AM -0500, Kim Phillips escreveu:
> Introduce new tools/perf/arch/*/util/evsel.c:perf_evsel__suppl_strerror()

The naming... suppl for what? for the open operation? strerror() methods
are associated with another method, one for which it can use context
like who is the user asking for that operation, procfs/sysfs knobs,
hardware, etc, so we need to have CLASS__METHOD_strerror()

In this case, CLASS == perf_evsel, METHOD = open, so, if you want to
have something that is _arch_ specific, we could use something like:

int __weak perf_evsel__open_strerror_arch(struct perf_evsel *evsel __maybe_unused,
					  struct target *target __maybe_unused,
					  int err __maybe_unused,
					  char *msg __maybe_unused,
					  size_t size __maybe_unused)
{
	return 0;
}

But then you're calling it _before_ the existing switch (err), humm...
I.e. it will add stuff before the string that will be formatted later...
The messages may end up being conflicting, I wonder if the model
wouldn't be better as: ask the arch specific if it wants to override
that specific error with something, if not, fallback to the existing
perf_evsel__open_strerror() code, that could be moved to be
__perf_evsel__open_strerror() and called by the arch specific code.

Thoughts?

- Arnaldo

_

> so each arch can start to customize usability for its h/w PMU drivers.
> 
> Signed-off-by: Kim Phillips <[email-masked]>
> ---
>  tools/perf/arch/x86/util/Build   |  1 +
>  tools/perf/arch/x86/util/evsel.c | 24 ++++++++++++++++++++++++
>  tools/perf/util/evsel.c          | 21 +++++++++++++++------
>  tools/perf/util/evsel.h          |  2 ++
>  4 files changed, 42 insertions(+), 6 deletions(-)
>  create mode 100644 tools/perf/arch/x86/util/evsel.c
> 
> diff --git a/tools/perf/arch/x86/util/Build b/tools/perf/arch/x86/util/Build
> index f95e6f46ef0d..90ae9358ec21 100644
> --- a/tools/perf/arch/x86/util/Build
> +++ b/tools/perf/arch/x86/util/Build
> @@ -4,6 +4,7 @@ libperf-y += pmu.o
>  libperf-y += kvm-stat.o
>  libperf-y += perf_regs.o
>  libperf-y += group.o
> +libperf-y += evsel.o
>  
>  libperf-$(CONFIG_DWARF) += dwarf-regs.o
>  libperf-$(CONFIG_BPF_PROLOGUE) += dwarf-regs.o
> diff --git a/tools/perf/arch/x86/util/evsel.c b/tools/perf/arch/x86/util/evsel.c
> new file mode 100644
> index 000000000000..95c623c0119f
> --- /dev/null
> +++ b/tools/perf/arch/x86/util/evsel.c
> @@ -0,0 +1,24 @@
> +#include <string.h>
> +
> +#include <linux/perf_event.h>
> +#include <linux/err.h>
> +
> +#include "../../util/evsel.h"
> +
> +int perf_evsel__suppl_strerror(struct perf_evsel *evsel,
> +			       struct target *target __maybe_unused,
> +			       int err, char *msg, size_t size)
> +{
> +	switch (err) {
> +	case EOPNOTSUPP:
> +		if (evsel->attr.type == PERF_TYPE_HARDWARE)
> +			return scnprintf(msg, size, "%s",
> +	"No hardware sampling interrupt available.\n"
> +	"No APIC? If so then you can boot the kernel with the \"lapic\" boot parameter to force-enable it.");
> +		break;
> +	default:
> +		break;
> +	}
> +
> +	return 0;
> +}
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 3ec0aed0bdcb..a6aa18e3a0c2 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2686,12 +2686,27 @@ static bool find_process(const char *name)
>  	return ret ? false : true;
>  }
>  
> +int __weak perf_evsel__suppl_strerror(struct perf_evsel *evsel __maybe_unused,
> +				      struct target *target __maybe_unused,
> +				      int err __maybe_unused,
> +				      char *msg __maybe_unused,
> +				      size_t size __maybe_unused)
> +{
> +	return 0;
> +}
> +
>  int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,
>  			      int err, char *msg, size_t size)
>  {
>  	char sbuf[STRERR_BUFSIZE];
>  	int printed = 0;
>  
> +	printed = perf_evsel__suppl_strerror(evsel, target, err, msg, size);
> +	if (printed > 0) {
> +		msg += printed;
> +		size -= printed;
> +	}
> +
>  	switch (err) {
>  	case EPERM:
>  	case EACCES:
> @@ -2745,12 +2760,6 @@ int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,
>  		if (evsel->attr.precise_ip)
>  			return scnprintf(msg, size, "%s",
>  	"\'precise\' request may not be supported. Try removing 'p' modifier.");
> -#if defined(__i386__) || defined(__x86_64__)
> -		if (evsel->attr.type == PERF_TYPE_HARDWARE)
> -			return scnprintf(msg, size, "%s",
> -	"No hardware sampling interrupt available.\n"
> -	"No APIC? If so then you can boot the kernel with the \"lapic\" boot parameter to force-enable it.");
> -#endif
>  		break;
>  	case EBUSY:
>  		if (find_process("oprofiled"))
> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> index 77bd310eb0cb..aef759c178aa 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -416,6 +416,8 @@ bool perf_evsel__fallback(struct perf_evsel *evsel, int err,
>  			  char *msg, size_t msgsize);
>  int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,
>  			      int err, char *msg, size_t size);
> +int perf_evsel__suppl_strerror(struct perf_evsel *evsel, struct target *target,
> +			       int err, char *msg, size_t size);
>  
>  static inline int perf_evsel__group_idx(struct perf_evsel *evsel)
>  {
> -- 
> 2.14.2