[PATCH v2 1/4] perf expr: Add debug logging for literals

[PATCH v2 1/4] perf expr: Add debug logging for literals

[Ian Rogers]

Useful for diagnosing problems with metrics.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/expr.c | 35 ++++++++++++++++++++++++-----------
 1 file changed, 24 insertions(+), 11 deletions(-)

diff --git a/tools/perf/util/expr.c b/tools/perf/util/expr.c
index 1d532b9fed29..cdbab4f959fe 100644
--- a/tools/perf/util/expr.c
+++ b/tools/perf/util/expr.c
@@ -395,12 +395,17 @@ double expr_id_data__source_count(const struct expr_id_data *data)
 double expr__get_literal(const char *literal)
 {
 	static struct cpu_topology *topology;
+	double result = NAN;
 
-	if (!strcmp("#smt_on", literal))
-		return smt_on() > 0 ? 1.0 : 0.0;
+	if (!strcmp("#smt_on", literal)) {
+		result =  smt_on() > 0 ? 1.0 : 0.0;
+		goto out;
+	}
 
-	if (!strcmp("#num_cpus", literal))
-		return cpu__max_present_cpu();
+	if (!strcmp("#num_cpus", literal)) {
+		result = cpu__max_present_cpu();
+		goto out;
+	}
 
 	/*
 	 * Assume that topology strings are consistent, such as CPUs "0-1"
@@ -415,13 +420,21 @@ double expr__get_literal(const char *literal)
 			return NAN;
 		}
 	}
-	if (!strcmp("#num_packages", literal))
-		return topology->package_cpus_lists;
-	if (!strcmp("#num_dies", literal))
-		return topology->die_cpus_lists;
-	if (!strcmp("#num_cores", literal))
-		return topology->core_cpus_lists;
+	if (!strcmp("#num_packages", literal)) {
+		result = topology->package_cpus_lists;
+		goto out;
+	}
+	if (!strcmp("#num_dies", literal)) {
+		result = topology->die_cpus_lists;
+		goto out;
+	}
+	if (!strcmp("#num_cores", literal)) {
+		result = topology->core_cpus_lists;
+		goto out;
+	}
 
 	pr_err("Unrecognized literal '%s'", literal);
-	return NAN;
+out:
+	pr_debug2("literal: %s = %f\n", literal, result);
+	return result;
 }
-- 
2.34.0.rc2.393.gf8c9666880-goog

[PATCH v2 2/4] perf tools: Fix SMT not detected

[Ian Rogers]

sysfs__read_int returns 0 on success, and so the fast read path was
always failing.

Fixes: bb629484d924 (perf tools: Simplify checking if SMT is active.)
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/smt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
index 20bacd5972ad..34f1b1b1176c 100644
--- a/tools/perf/util/smt.c
+++ b/tools/perf/util/smt.c
@@ -15,7 +15,7 @@ int smt_on(void)
 	if (cached)
 		return cached_result;
 
-	if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) > 0)
+	if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) >= 0)
 		goto done;
 
 	ncpu = sysconf(_SC_NPROCESSORS_CONF);
-- 
2.34.0.rc2.393.gf8c9666880-goog

Re: [PATCH v2 2/4] perf tools: Fix SMT not detected

[John Garry]

On 24/11/2021 00:12, Ian Rogers wrote:
> sysfs__read_int returns 0 on success, and so the fast read path was
> always failing.
> 
> Fixes: bb629484d924 (perf tools: Simplify checking if SMT is active.)
> Signed-off-by: Ian Rogers<irogers@google.com>
> ---

Reviewed-by: John Garry <john.garry@huawei.com>

Re: [PATCH v2 2/4] perf tools: Fix SMT not detected

[Arnaldo Carvalho de Melo]

Em Tue, Nov 23, 2021 at 04:12:29PM -0800, Ian Rogers escreveu:
> sysfs__read_int returns 0 on success, and so the fast read path was
> always failing.
> 
> Fixes: bb629484d924 (perf tools: Simplify checking if SMT is active.)
> Signed-off-by: Ian Rogers <irogers@google.com>

Thanks, applied to perf/urgent.

- Arnaldo

> ---
>  tools/perf/util/smt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
> index 20bacd5972ad..34f1b1b1176c 100644
> --- a/tools/perf/util/smt.c
> +++ b/tools/perf/util/smt.c
> @@ -15,7 +15,7 @@ int smt_on(void)
>  	if (cached)
>  		return cached_result;
>  
> -	if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) > 0)
> +	if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) >= 0)
>  		goto done;
>  
>  	ncpu = sysconf(_SC_NPROCESSORS_CONF);
> -- 
> 2.34.0.rc2.393.gf8c9666880-goog

-- 

- Arnaldo

[PATCH v2 3/4] perf tools: Fix SMT fallback with large core counts

[Ian Rogers]

strtoull can only read a 64-bit bitmap. On an AMD EPYC core_cpus may look
like:
00000000,00000000,00000000,00000001,00000000,00000000,00000000,00000001
and so the sibling wasn't spotted. Fix by writing a simple hweight string
parser.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/smt.c | 68 ++++++++++++++++++++++++++++++++++++-------
 1 file changed, 58 insertions(+), 10 deletions(-)

diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
index 34f1b1b1176c..2636be65305a 100644
--- a/tools/perf/util/smt.c
+++ b/tools/perf/util/smt.c
@@ -5,6 +5,56 @@
 #include "api/fs/fs.h"
 #include "smt.h"
 
+/**
+ * hweight_str - Returns the number of bits set in str. Stops at first non-hex
+ *	       or ',' character.
+ */
+static int hweight_str(char *str)
+{
+	int result = 0;
+
+	while (*str) {
+		switch (*str++) {
+		case '0':
+		case ',':
+			break;
+		case '1':
+		case '2':
+		case '4':
+		case '8':
+			result++;
+			break;
+		case '3':
+		case '5':
+		case '6':
+		case '9':
+		case 'a':
+		case 'A':
+		case 'c':
+		case 'C':
+			result += 2;
+			break;
+		case '7':
+		case 'b':
+		case 'B':
+		case 'd':
+		case 'D':
+		case 'e':
+		case 'E':
+			result += 3;
+			break;
+		case 'f':
+		case 'F':
+			result += 4;
+			break;
+		default:
+			goto done;
+		}
+	}
+done:
+	return result;
+}
+
 int smt_on(void)
 {
 	static bool cached;
@@ -15,9 +65,12 @@ int smt_on(void)
 	if (cached)
 		return cached_result;
 
-	if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) >= 0)
-		goto done;
+	if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) >= 0) {
+		cached = true;
+		return cached_result;
+	}
 
+	cached_result = 0;
 	ncpu = sysconf(_SC_NPROCESSORS_CONF);
 	for (cpu = 0; cpu < ncpu; cpu++) {
 		unsigned long long siblings;
@@ -35,18 +88,13 @@ int smt_on(void)
 				continue;
 		}
 		/* Entry is hex, but does not have 0x, so need custom parser */
-		siblings = strtoull(str, NULL, 16);
+		siblings = hweight_str(str);
 		free(str);
-		if (hweight64(siblings) > 1) {
+		if (siblings > 1) {
 			cached_result = 1;
-			cached = true;
 			break;
 		}
 	}
-	if (!cached) {
-		cached_result = 0;
-done:
-		cached = true;
-	}
+	cached = true;
 	return cached_result;
 }
-- 
2.34.0.rc2.393.gf8c9666880-goog

Re: [PATCH v2 3/4] perf tools: Fix SMT fallback with large core counts

[John Garry]

On 24/11/2021 00:12, Ian Rogers wrote:
> strtoull can only read a 64-bit bitmap. On an AMD EPYC core_cpus may look
> like:
> 00000000,00000000,00000000,00000001,00000000,00000000,00000000,00000001
> and so the sibling wasn't spotted. Fix by writing a simple hweight string
> parser.
> 
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>   tools/perf/util/smt.c | 68 ++++++++++++++++++++++++++++++++++++-------
>   1 file changed, 58 insertions(+), 10 deletions(-)
> 
> diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
> index 34f1b1b1176c..2636be65305a 100644
> --- a/tools/perf/util/smt.c
> +++ b/tools/perf/util/smt.c
> @@ -5,6 +5,56 @@
>   #include "api/fs/fs.h"
>   #include "smt.h"
>   
> +/**
> + * hweight_str - Returns the number of bits set in str. Stops at first non-hex
> + *	       or ',' character.

nit: the wording here could be improved, I think. You really mean we 
iter until we reach a character which is neither a hex nor a ',', while 
I read this as iter until either a non-hex or a ','.

> + */
> +static int hweight_str(char *str)
> +{
> +	int result = 0;
> +
> +	while (*str) {

Can we use __buitin_popcount() to try to simplify?

> +		switch (*str++) {
> +		case '0':
> +		case ',':
> +			break;
> +		case '1':
> +		case '2':
> +		case '4':
> +		case '8':
> +			result++;
> +			break;
> +		case '3':
> +		case '5':
> +		case '6':
> +		case '9':
> +		case 'a':
> +		case 'A':
> +		case 'c':
> +		case 'C':
> +			result += 2;
> +			break;
> +		case '7':
> +		case 'b':
> +		case 'B':
> +		case 'd':
> +		case 'D':
> +		case 'e':
> +		case 'E':
> +			result += 3;
> +			break;
> +		case 'f':
> +		case 'F':
> +			result += 4;
> +			break;
> +		default:
> +			goto done;
> +		}
> +	}
> +done:

[PATCH v2 4/4] perf tools: Probe non-deprecated sysfs path 1st

[Ian Rogers]

Following Documentation/ABI/stable/sysfs-devices-system-cpu the
/sys/devices/system/cpu/cpuX/topology/core_cpus is deprecated in favor
of thread_siblings, so probe thread_siblings before falling back on
core_cpus.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/smt.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
index 2636be65305a..2b0a36ebf27a 100644
--- a/tools/perf/util/smt.c
+++ b/tools/perf/util/smt.c
@@ -79,11 +79,10 @@ int smt_on(void)
 		char fn[256];
 
 		snprintf(fn, sizeof fn,
-			"devices/system/cpu/cpu%d/topology/core_cpus", cpu);
+			"devices/system/cpu/cpu%d/topology/thread_siblings", cpu);
 		if (sysfs__read_str(fn, &str, &strlen) < 0) {
 			snprintf(fn, sizeof fn,
-				"devices/system/cpu/cpu%d/topology/thread_siblings",
-				cpu);
+				"devices/system/cpu/cpu%d/topology/core_cpus", cpu);
 			if (sysfs__read_str(fn, &str, &strlen) < 0)
 				continue;
 		}
-- 
2.34.0.rc2.393.gf8c9666880-goog

Re: [PATCH v2 1/4] perf expr: Add debug logging for literals

[John Garry]

>   	}
> -	if (!strcmp("#num_packages", literal))
> -		return topology->package_cpus_lists;
> -	if (!strcmp("#num_dies", literal))
> -		return topology->die_cpus_lists;
> -	if (!strcmp("#num_cores", literal))
> -		return topology->core_cpus_lists;
> +	if (!strcmp("#num_packages", literal)) {
> +		result = topology->package_cpus_lists;
> +		goto out;
> +	}
> +	if (!strcmp("#num_dies", literal)) {
> +		result = topology->die_cpus_lists;
> +		goto out;
> +	}
> +	if (!strcmp("#num_cores", literal)) {
> +		result = topology->core_cpus_lists;

if we find that we now get the same print many times, how about:
		pr_debug2_once("literal: num_cores = %f\n", result);

... not sure if it scales though

Thanks,
John


> +		goto out;
> +	}
>   
>   	pr_err("Unrecognized literal '%s'", literal);
> -	return NAN;
> +out:
> +	pr_debug2("literal: %s = %f\n", literal, result);
> +	return result;
>   }