Re: [PATCH v6 4/6] perf jevents: Add a new expression builtin strcmp_cpuid_str()

From: Ian Rogers
Date: Tue Aug 29 2023 - 19:48:01 EST

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On Wed, Aug 16, 2023 at 4:52 AM James Clark <james.clark@xxxxxxx> wrote:
>
> This will allow writing formulas that are conditional on a specific
> CPU type or CPU version. It calls through to the existing
> strcmp_cpuid_str() function in Perf which has a default weak version,
> and an arch specific version for x86 and arm64.
>
> The function takes an 'ID' type value, which is a string. But in this
> case Arm CPU IDs are hex numbers prefixed with '0x'. metric.py
> assumes strings are only used by event names, and that they can't start
> with a number ('0'), so an additional change has to be made to the
> regex to convert hex numbers back to 'ID' types.
>
> Signed-off-by: James Clark <james.clark@xxxxxxx>
> ---
> tools/perf/arch/arm64/util/pmu.c | 18 +-----------------
> tools/perf/pmu-events/metric.py | 17 +++++++++++++++--
> tools/perf/util/expr.c | 18 ++++++++++++++++++
> tools/perf/util/expr.h | 1 +
> tools/perf/util/expr.l | 1 +
> tools/perf/util/expr.y | 8 +++++++-
> tools/perf/util/pmu.c | 17 +++++++++++++++++
> tools/perf/util/pmu.h | 1 +
> 8 files changed, 61 insertions(+), 20 deletions(-)
>
> diff --git a/tools/perf/arch/arm64/util/pmu.c b/tools/perf/arch/arm64/util/pmu.c
> index 512a8f13c4de..615084eb88d8 100644
> --- a/tools/perf/arch/arm64/util/pmu.c
> +++ b/tools/perf/arch/arm64/util/pmu.c
> @@ -2,28 +2,12 @@
>
> #include <internal/cpumap.h>
> #include "../../../util/cpumap.h"
> +#include "../../../util/header.h"
> #include "../../../util/pmu.h"
> #include "../../../util/pmus.h"
> #include <api/fs/fs.h>
> #include <math.h>
>
> -static struct perf_pmu *pmu__find_core_pmu(void)
> -{
> - struct perf_pmu *pmu = NULL;
> -
> - while ((pmu = perf_pmus__scan_core(pmu))) {
> - /*
> - * The cpumap should cover all CPUs. Otherwise, some CPUs may
> - * not support some events or have different event IDs.
> - */
> - if (RC_CHK_ACCESS(pmu->cpus)->nr != cpu__max_cpu().cpu)
> - return NULL;
> -
> - return pmu;
> - }
> - return NULL;
> -}
> -
> const struct pmu_metrics_table *pmu_metrics_table__find(void)
> {
> struct perf_pmu *pmu = pmu__find_core_pmu();
> diff --git a/tools/perf/pmu-events/metric.py b/tools/perf/pmu-events/metric.py
> index 85a3545f5b6a..0e9ec65d92ae 100644
> --- a/tools/perf/pmu-events/metric.py
> +++ b/tools/perf/pmu-events/metric.py
> @@ -413,6 +413,10 @@ def has_event(event: Event) -> Function:
> # pylint: disable=invalid-name
> return Function('has_event', event)
>
> +def strcmp_cpuid_str(event: str) -> Function:
> + # pylint: disable=redefined-builtin
> + # pylint: disable=invalid-name
> + return Function('strcmp_cpuid_str', event)
>
> class Metric:
> """An individual metric that will specifiable on the perf command line."""
> @@ -541,14 +545,23 @@ def ParsePerfJson(orig: str) -> Expression:
> """
> # pylint: disable=eval-used
> py = orig.strip()
> + # First try to convert everything that looks like a string (event name) into Event(r"EVENT_NAME").
> + # This isn't very selective so is followed up by converting some unwanted conversions back again
> py = re.sub(r'([a-zA-Z][^-+/\* \\,]*(?:\\.[^-+/\* \\,]*)*)',
> r'Event(r"\1")', py)
> + # If it started with a # it should have been a literal, rather than an event name
> py = re.sub(r'#Event$r"([^"]*)"$', r'Literal("#\1")', py)
> + # Convert accidentally converted hex constants ("0Event(r"xDEADBEEF)"") back to a constant,
> + # but keep it wrapped in Event(), otherwise Python drops the 0x prefix and it gets interpreted as
> + # a double by the Bison parser
> + py = re.sub(r'0Event$r"[xX]([0-9a-fA-F]*)"$', r'Event("0x\1")', py)
> + # Convert accidentally converted scientific notation constants back
> py = re.sub(r'([0-9]+)Event$r"(e[0-9]+)"$', r'\1\2', py)
> - keywords = ['if', 'else', 'min', 'max', 'd_ratio', 'source_count', 'has_event']
> + # Convert all the known keywords back from events to just the keyword
> + keywords = ['if', 'else', 'min', 'max', 'd_ratio', 'source_count', 'has_event', 'strcmp_cpuid_str',
> + 'cpuid_not_more_than']
> for kw in keywords:
> py = re.sub(rf'Event$r"{kw}"$', kw, py)
> -
> try:
> parsed = ast.parse(py, mode='eval')
> except SyntaxError as e:
> diff --git a/tools/perf/util/expr.c b/tools/perf/util/expr.c
> index 7410a165f68b..0985a3cbc6f9 100644
> --- a/tools/perf/util/expr.c
> +++ b/tools/perf/util/expr.c
> @@ -13,6 +13,8 @@
> #include <util/expr-bison.h>
> #include <util/expr-flex.h>
> #include "util/hashmap.h"
> +#include "util/header.h"
> +#include "util/pmu.h"
> #include "smt.h"
> #include "tsc.h"
> #include <api/fs/fs.h>
> @@ -495,3 +497,19 @@ double expr__has_event(const struct expr_parse_ctx *ctx, bool compute_ids, const
> evlist__delete(tmp);
> return ret;
> }
> +
> +double expr__strcmp_cpuid_str(const struct expr_parse_ctx *ctx __maybe_unused,
> + bool compute_ids __maybe_unused, const char *test_id)
> +{
> + double ret;
> + struct perf_pmu *pmu = pmu__find_core_pmu();
> + char *cpuid = perf_pmu__getcpuid(pmu);
> +
> + if (!cpuid)
> + return NAN;
> +
> + ret = !strcmp_cpuid_str(test_id, cpuid);
> +
> + free(cpuid);
> + return ret;
> +}
> diff --git a/tools/perf/util/expr.h b/tools/perf/util/expr.h
> index 3c1e49b3e35d..c0cec29ddc29 100644
> --- a/tools/perf/util/expr.h
> +++ b/tools/perf/util/expr.h
> @@ -55,5 +55,6 @@ double expr_id_data__value(const struct expr_id_data *data);
> double expr_id_data__source_count(const struct expr_id_data *data);
> double expr__get_literal(const char *literal, const struct expr_scanner_ctx *ctx);
> double expr__has_event(const struct expr_parse_ctx *ctx, bool compute_ids, const char *id);
> +double expr__strcmp_cpuid_str(const struct expr_parse_ctx *ctx, bool compute_ids, const char *id);
>
> #endif
> diff --git a/tools/perf/util/expr.l b/tools/perf/util/expr.l
> index dbb117414710..0feef0726c48 100644
> --- a/tools/perf/util/expr.l
> +++ b/tools/perf/util/expr.l
> @@ -114,6 +114,7 @@ if { return IF; }
> else { return ELSE; }
> source_count { return SOURCE_COUNT; }
> has_event { return HAS_EVENT; }
> +strcmp_cpuid_str { return STRCMP_CPUID_STR; }

For the sake of coverage, it'd be nice to have a test case like:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/tests/expr.c?h=tmp.perf-tools-next#n257

> {literal} { return literal(yyscanner, sctx); }
> {number} { return value(yyscanner); }
> {symbol} { return str(yyscanner, ID, sctx->runtime); }
> diff --git a/tools/perf/util/expr.y b/tools/perf/util/expr.y
> index 65d54a6f29ad..6c93b358cc2d 100644
> --- a/tools/perf/util/expr.y
> +++ b/tools/perf/util/expr.y
> @@ -39,7 +39,7 @@ int expr_lex(YYSTYPE * yylval_param , void *yyscanner);
> } ids;
> }
>
> -%token ID NUMBER MIN MAX IF ELSE LITERAL D_RATIO SOURCE_COUNT HAS_EVENT EXPR_ERROR
> +%token ID NUMBER MIN MAX IF ELSE LITERAL D_RATIO SOURCE_COUNT HAS_EVENT STRCMP_CPUID_STR EXPR_ERROR
> %left MIN MAX IF
> %left '|'
> %left '^'
> @@ -207,6 +207,12 @@ expr: NUMBER
> $$.ids = NULL;
> free($3);
> }
> +| STRCMP_CPUID_STR '(' ID ')'
> +{
> + $$.val = expr__strcmp_cpuid_str(ctx, compute_ids, $3);
> + $$.ids = NULL;
> + free($3);
> +}
> | expr '|' expr
> {
> if (is_const($1.val) && is_const($3.val)) {
> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
> index d5406effc169..a7f05e4dda97 100644
> --- a/tools/perf/util/pmu.c
> +++ b/tools/perf/util/pmu.c
> @@ -1790,3 +1790,20 @@ void perf_pmu__delete(struct perf_pmu *pmu)
> zfree(&pmu->alias_name);
> free(pmu);
> }
> +
> +struct perf_pmu *pmu__find_core_pmu(void)

I think as this is scanning all PMUs it more logically belongs in
pmus.c than pmu.c.

> +{
> + struct perf_pmu *pmu = NULL;
> +
> + while ((pmu = perf_pmus__scan_core(pmu))) {
> + /*
> + * The cpumap should cover all CPUs. Otherwise, some CPUs may
> + * not support some events or have different event IDs.
> + */
> + if (RC_CHK_ACCESS(pmu->cpus)->nr != cpu__max_cpu().cpu)

The RC_CHK_ACCESS can be avoided using perf_cpu_map__nr.

Not all CPUs need to be online. I think the number for the PMU is
bound by the number online while cpu__max_cpu gives the maximum
present. It is common to workaround SMT vulnerabilities by making
cores offline in which case this would never be true. I think the
following is nearly equivalent and simpler:

perf_pmus__num_core_pmus > 1 ? NULL : perf_pmus__scan_core(NULL);

Thanks,
Ian

> + return NULL;
> +
> + return pmu;
> + }
> + return NULL;
> +}
> diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
> index 6b414cecbad2..7ff925224165 100644
> --- a/tools/perf/util/pmu.h
> +++ b/tools/perf/util/pmu.h
> @@ -289,5 +289,6 @@ int perf_pmu__pathname_fd(int dirfd, const char *pmu_name, const char *filename,
> struct perf_pmu *perf_pmu__lookup(struct list_head *pmus, int dirfd, const char *lookup_name);
> struct perf_pmu *perf_pmu__create_placeholder_core_pmu(struct list_head *core_pmus);
> void perf_pmu__delete(struct perf_pmu *pmu);
> +struct perf_pmu *pmu__find_core_pmu(void);
>
> #endif /* __PMU_H */
> --
> 2.34.1
>

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