Re: [PATCH v2 8/9] perf metrics: Add has_optane literal

["Liang, Kan" <kan.liang@linux.intel.com>]

On 2023-03-23 3:20 p.m., Ian Rogers wrote:
> Add literal so that if optane memory isn't installed we can record
> fewer events.  

I think we call it pmem (Persistent Memory) everywhere in the Linux
code. Maybe we should use #has_pmem instead?

Thanks,
Kan
> The file detection mechanism was suggested by Dan
> Williams <dan.j.williams@intel.com> in:
> https://lore.kernel.org/linux-perf-users/641bbe1eced26_1b98bb29440@dwillia2-xfh.jf.intel.com.notmuch/
> 
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/perf/util/expr.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/tools/perf/util/expr.c b/tools/perf/util/expr.c
> index d46a1878bc9e..a43cdda0b044 100644
> --- a/tools/perf/util/expr.c
> +++ b/tools/perf/util/expr.c
> @@ -14,6 +14,7 @@
>  #include "util/hashmap.h"
>  #include "smt.h"
>  #include "tsc.h"
> +#include <api/fs/fs.h>
>  #include <linux/err.h>
>  #include <linux/kernel.h>
>  #include <linux/zalloc.h>
> @@ -400,6 +401,20 @@ double arch_get_tsc_freq(void)
>  }
>  #endif
>  
> +static double has_optane(void)
> +{
> +	static bool has_optane, cached;
> +	const char *sysfs = sysfs__mountpoint();
> +	char path[PATH_MAX];
> +
> +	if (!cached) {
> +		snprintf(path, sizeof(path), "%s/firmware/acpi/tables/NFIT", sysfs);
> +		has_optane = access(path, F_OK) == 0;
> +		cached = true;
> +	}
> +	return has_optane ? 1.0 : 0.0;
> +}
> +
>  double expr__get_literal(const char *literal, const struct expr_scanner_ctx *ctx)
>  {
>  	const struct cpu_topology *topology;
> @@ -449,6 +464,10 @@ double expr__get_literal(const char *literal, const struct expr_scanner_ctx *ctx
>  		result = perf_pmu__cpu_slots_per_cycle();
>  		goto out;
>  	}
> +	if (!strcmp("#has_optane", literal)) {
> +		result = has_optane();
> +		goto out;
> +	}
>  
>  	pr_err("Unrecognized literal '%s'", literal);
>  out: