Re: [PATCH 6/7] perf expr: Add metric literals for topology.

[Ian Rogers <irogers@google.com>]

On Wed, Nov 10, 2021 at 6:35 AM Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Wed, Nov 10, 2021 at 06:19:04AM -0800, Ian Rogers wrote:
> > On Wed, Nov 10, 2021 at 4:56 AM Jiri Olsa <jolsa@redhat.com> wrote:
> > >
> > > On Fri, Nov 05, 2021 at 10:09:42AM -0700, Ian Rogers wrote:
> > > > Allow the number of cpus, cores, dies and packages to be queried by a
> > > > metric expression.
> > > >
> > > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > > ---
> > > >  tools/perf/tests/expr.c | 12 +++++++++++-
> > > >  tools/perf/util/expr.c  | 27 +++++++++++++++++++++++++++
> > > >  2 files changed, 38 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/tools/perf/tests/expr.c b/tools/perf/tests/expr.c
> > > > index 9ee2dc91c27b..0c09ccc76665 100644
> > > > --- a/tools/perf/tests/expr.c
> > > > +++ b/tools/perf/tests/expr.c
> > > > @@ -66,7 +66,7 @@ int test__expr(struct test *t __maybe_unused, int subtest __maybe_unused)
> > > >  {
> > > >       struct expr_id_data *val_ptr;
> > > >       const char *p;
> > > > -     double val;
> > > > +     double val, num_cpus, num_cores, num_dies, num_packages;
> > > >       int ret;
> > > >       struct expr_parse_ctx *ctx;
> > > >
> > > > @@ -161,6 +161,16 @@ int test__expr(struct test *t __maybe_unused, int subtest __maybe_unused)
> > > >                       NULL, ctx) == 0);
> > > >       TEST_ASSERT_VAL("find ids", hashmap__size(ctx->ids) == 0);
> > > >
> > > > +     /* Test toplogy constants appear well ordered. */
> > > > +     expr__ctx_clear(ctx);
> > > > +     TEST_ASSERT_VAL("#num_cpus", expr__parse(&num_cpus, ctx, "#num_cpus") == 0);
> > > > +     TEST_ASSERT_VAL("#num_cores", expr__parse(&num_cores, ctx, "#num_cores") == 0);
> > > > +     TEST_ASSERT_VAL("#num_cpus >= #num_cores", num_cpus >= num_cores);
> > > > +     TEST_ASSERT_VAL("#num_dies", expr__parse(&num_dies, ctx, "#num_dies") == 0);
> > > > +     TEST_ASSERT_VAL("#num_cores >= #num_dies", num_cores >= num_dies);
> > > > +     TEST_ASSERT_VAL("#num_packages", expr__parse(&num_packages, ctx, "#num_packages") == 0);
> > > > +     TEST_ASSERT_VAL("#num_dies >= #num_packages", num_dies >= num_packages);
> > > > +
> > > >       expr__ctx_free(ctx);
> > > >
> > > >       return 0;
> > > > diff --git a/tools/perf/util/expr.c b/tools/perf/util/expr.c
> > > > index 7464739c2890..15af8b8ef5e7 100644
> > > > --- a/tools/perf/util/expr.c
> > > > +++ b/tools/perf/util/expr.c
> > > > @@ -5,6 +5,8 @@
> > > >  #include <stdlib.h>
> > > >  #include <string.h>
> > > >  #include "metricgroup.h"
> > > > +#include "cpumap.h"
> > > > +#include "cputopo.h"
> > > >  #include "debug.h"
> > > >  #include "expr.h"
> > > >  #include "expr-bison.h"
> > > > @@ -375,9 +377,34 @@ double expr_id_data__value(const struct expr_id_data *data)
> > > >
> > > >  double expr__get_literal(const char *literal)
> > > >  {
> > > > +     static struct cpu_topology *topology;
> > > > +
> > > >       if (!strcmp("#smt_on", literal))
> > > >               return smt_on() > 0 ? 1.0 : 0.0;
> > > >
> > > > +     if (!strcmp("#num_cpus", literal))
> > > > +             return cpu__max_present_cpu();
> > > > +
> > > > +     /*
> > > > +      * Assume that topology strings are consistent, such as CPUs "0-1"
> > > > +      * wouldn't be listed as "0,1", and so after deduplication the number of
> > > > +      * these strings gives an indication of the number of packages, dies,
> > > > +      * etc.
> > > > +      */
> > > > +     if (!topology) {
> > > > +             topology = cpu_topology__new();
> > >
> > > any chance we could propagate expr_scanner_ctx in here and store topology
> > > to it and release it at the end? I think we have several places like this,
> > > so it'd be nice not to make more if it's possible ;-)
> >
> > The topology here is static and so will only get computed once per
> > execution rather than once pre expression parse. I was worried about
> > the cost of recomputing the topology for something like 'perf stat -I
> > 1000 -M ...' in which case the static will do less recomputation.
>
> can't we have the topology created/release on the top fo the parsing
> and released after all expressions are parsed?
>
> or we could come up with some generic way to handle this kind of release

Creating the topology at the top of metric parsing would incur a sysfs
parsing cost on metrics regardless of whether they used the topology.
I feel a lazy approach is better to avoid this cost. We could make
this part of the expression context and lazily initialize it there.
It'd be good to keep the expression context around in 'perf stat' in
that case. I quite like this approach as really the topology should be
part of the perf environment and part of the header. It is interesting
to think how can we get metrics to work with 'perf stat record'.
Currently you will get metrics for something like 'perf stat record -e
instructions,cycles -a sleep 2; perf stat report', but none baked in
metrics don't work and we don't even have the metric-id to make this
work (even using '-M IPC' doesn't work). Putting the environment in
the session, making the topology part of it, writing/reading data
based on that seems like worthwhile clean up but beyond the scope of
what I was trying to do here.

In terms of releasing for the sake of memory leaks, leak sanitizer
doesn't treat memory allocated and reachable from a global as a leak.
We can't precompute the topology and so this style of approach is what
I'm used to. Putting the topology into the parsing context and lazily
initializing would be the second best option imo, and I can do that if
this is a blocker.

Thanks,
Ian

> jirka
>
> >
> > Thanks,
> > Ian
> >
> > > thanks,
> > > jirka
> > >
> > > > +             if (!topology) {
> > > > +                     pr_err("Error creating CPU topology");
> > > > +                     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;
> > > > +
> > > >       pr_err("Unrecognized literal '%s'", literal);
> > > >       return NAN;
> > > >  }
> > > > --
> > > > 2.34.0.rc0.344.g81b53c2807-goog
> > > >
> > >
> >
>