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Message-ID: <CAP-5=fU7pVjaabBq4xuPsDw9oYk9Cf2kWF+x58uRYCY2XX13Nw@mail.gmail.com>
Date: Mon, 9 Dec 2024 14:23:49 -0800
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>, Kan Liang <kan.liang@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>,
LKML <linux-kernel@...r.kernel.org>, linux-perf-users@...r.kernel.org,
Andrii Nakryiko <andrii@...nel.org>, Song Liu <song@...nel.org>, bpf@...r.kernel.org,
Stephane Eranian <eranian@...gle.com>, Vlastimil Babka <vbabka@...e.cz>,
Roman Gushchin <roman.gushchin@...ux.dev>, Hyeonggon Yoo <42.hyeyoo@...il.com>,
Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v2 2/4] perf lock contention: Run BPF slab cache iterator
On Mon, Dec 9, 2024 at 2:16 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Mon, Dec 09, 2024 at 01:38:39PM -0300, Arnaldo Carvalho de Melo wrote:
> > On Mon, Dec 09, 2024 at 01:36:52PM -0300, Arnaldo Carvalho de Melo wrote:
> > > On Thu, Nov 07, 2024 at 10:14:57PM -0800, Namhyung Kim wrote:
> > > > Recently the kernel got the kmem_cache iterator to traverse metadata of
> > > > slab objects. This can be used to symbolize dynamic locks in a slab.
> > > >
> > > > The new slab_caches hash map will have the pointer of the kmem_cache as
> > > > a key and save the name and a id. The id will be saved in the flags
> > > > part of the lock.
> > >
> > > Trying to fix this
> >
> > So you have that struct in tools/perf/util/bpf_skel/vmlinux/vmlinux.h,
> > but then, this kernel is old and doesn't have the kmem_cache iterator,
> > so using the generated vmlinux.h will fail the build.
>
> Thanks for checking this. I think we handle compatibility issues by
> checking BTF at runtime but this is a build-time issue. :(
>
> I wonder if it's really needed to generate vmlinux.h for perf. Can we
> simply use the minimal vmlinux.h always?
Agreed, it shouldn't be necessary. There are certain compilation
errors that will happen with a generated one that can't happen with
the minimal. They could be indicative of bugs, like a renamed struct.
Thanks,
Ian
> >
> > > cd . && make GEN_VMLINUX_H=1 FEATURES_DUMP=/home/acme/git/perf-tools-next/tools/perf/BUILD_TEST_FEATURE_DUMP -j28 O=/tmp/tmp.DWo9tIFvWU DESTDIR=/tmp/tmp.ex3iljqLBT
> > > BUILD: Doing 'make -j28' parallel build
> [...]
> > > GEN /tmp/tmp.DWo9tIFvWU/util/bpf_skel/vmlinux.h
> > > CLANG /tmp/tmp.DWo9tIFvWU/util/bpf_skel/.tmp/bpf_prog_profiler.bpf.o
> > > CLANG /tmp/tmp.DWo9tIFvWU/util/bpf_skel/.tmp/bperf_leader.bpf.o
> > > CLANG /tmp/tmp.DWo9tIFvWU/util/bpf_skel/.tmp/bperf_follower.bpf.o
> > > CLANG /tmp/tmp.DWo9tIFvWU/util/bpf_skel/.tmp/bperf_cgroup.bpf.o
> > > CLANG /tmp/tmp.DWo9tIFvWU/util/bpf_skel/.tmp/func_latency.bpf.o
> > > CLANG /tmp/tmp.DWo9tIFvWU/util/bpf_skel/.tmp/off_cpu.bpf.o
> > > CLANG /tmp/tmp.DWo9tIFvWU/util/bpf_skel/.tmp/lock_contention.bpf.o
> > > CLANG /tmp/tmp.DWo9tIFvWU/util/bpf_skel/.tmp/kwork_trace.bpf.o
> > > CLANG /tmp/tmp.DWo9tIFvWU/util/bpf_skel/.tmp/sample_filter.bpf.o
> > > CLANG /tmp/tmp.DWo9tIFvWU/util/bpf_skel/.tmp/kwork_top.bpf.o
> > > CLANG /tmp/tmp.DWo9tIFvWU/util/bpf_skel/.tmp/bench_uprobe.bpf.o
> > > CLANG /tmp/tmp.DWo9tIFvWU/util/bpf_skel/.tmp/augmented_raw_syscalls.bpf.o
> > > GENSKEL /tmp/tmp.DWo9tIFvWU/util/bpf_skel/bench_uprobe.skel.h
> > > GENSKEL /tmp/tmp.DWo9tIFvWU/util/bpf_skel/func_latency.skel.h
> > > util/bpf_skel/lock_contention.bpf.c:612:28: error: declaration of 'struct bpf_iter__kmem_cache' will not be visible outside of this function [-Werror,-Wvisibility]
> > > 612 | int slab_cache_iter(struct bpf_iter__kmem_cache *ctx)
> > > | ^
> > > util/bpf_skel/lock_contention.bpf.c:614:28: error: incomplete definition of type 'struct bpf_iter__kmem_cache'
> > > 614 | struct kmem_cache *s = ctx->s;
> > > | ~~~^
> > > util/bpf_skel/lock_contention.bpf.c:612:28: note: forward declaration of 'struct bpf_iter__kmem_cache'
> > > 612 | int slab_cache_iter(struct bpf_iter__kmem_cache *ctx)
> > > | ^
> > > 2 errors generated.
> > > make[4]: *** [Makefile.perf:1248: /tmp/tmp.DWo9tIFvWU/util/bpf_skel/.tmp/lock_contention.bpf.o] Error 1
> > > make[4]: *** Waiting for unfinished jobs....
> > > make[3]: *** [Makefile.perf:292: sub-make] Error 2
> > > make[2]: *** [Makefile:76: all] Error 2
> > > make[1]: *** [tests/make:344: make_gen_vmlinux_h_O] Error 1
> > > make: *** [Makefile:109: build-test] Error 2
> > > make: Leaving directory '/home/acme/git/perf-tools-next/tools/perf'
> > >
> > > real 3m43.896s
> > > user 29m30.716s
> > > sys 6m36.609s
> > > ⬢ [acme@...lbox perf-tools-next]$
> > >
> > >
> > >
> > > > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > > > ---
> > > > tools/perf/util/bpf_lock_contention.c | 50 +++++++++++++++++++
> > > > .../perf/util/bpf_skel/lock_contention.bpf.c | 28 +++++++++++
> > > > tools/perf/util/bpf_skel/lock_data.h | 12 +++++
> > > > tools/perf/util/bpf_skel/vmlinux/vmlinux.h | 8 +++
> > > > 4 files changed, 98 insertions(+)
> > > >
> > > > diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
> > > > index 41a1ad08789511c3..558590c3111390fc 100644
> > > > --- a/tools/perf/util/bpf_lock_contention.c
> > > > +++ b/tools/perf/util/bpf_lock_contention.c
> > > > @@ -12,12 +12,59 @@
> > > > #include <linux/zalloc.h>
> > > > #include <linux/string.h>
> > > > #include <bpf/bpf.h>
> > > > +#include <bpf/btf.h>
> > > > #include <inttypes.h>
> > > >
> > > > #include "bpf_skel/lock_contention.skel.h"
> > > > #include "bpf_skel/lock_data.h"
> > > >
> > > > static struct lock_contention_bpf *skel;
> > > > +static bool has_slab_iter;
> > > > +
> > > > +static void check_slab_cache_iter(struct lock_contention *con)
> > > > +{
> > > > + struct btf *btf = btf__load_vmlinux_btf();
> > > > + s32 ret;
> > > > +
> > > > + if (btf == NULL) {
> > > > + pr_debug("BTF loading failed: %s\n", strerror(errno));
> > > > + return;
> > > > + }
> > > > +
> > > > + ret = btf__find_by_name_kind(btf, "bpf_iter__kmem_cache", BTF_KIND_STRUCT);
> > > > + if (ret < 0) {
> > > > + bpf_program__set_autoload(skel->progs.slab_cache_iter, false);
> > > > + pr_debug("slab cache iterator is not available: %d\n", ret);
> > > > + goto out;
> > > > + }
> > > > +
> > > > + has_slab_iter = true;
> > > > +
> > > > + bpf_map__set_max_entries(skel->maps.slab_caches, con->map_nr_entries);
> > > > +out:
> > > > + btf__free(btf);
> > > > +}
> > > > +
> > > > +static void run_slab_cache_iter(void)
> > > > +{
> > > > + int fd;
> > > > + char buf[256];
> > > > +
> > > > + if (!has_slab_iter)
> > > > + return;
> > > > +
> > > > + fd = bpf_iter_create(bpf_link__fd(skel->links.slab_cache_iter));
> > > > + if (fd < 0) {
> > > > + pr_debug("cannot create slab cache iter: %d\n", fd);
> > > > + return;
> > > > + }
> > > > +
> > > > + /* This will run the bpf program */
> > > > + while (read(fd, buf, sizeof(buf)) > 0)
> > > > + continue;
> > > > +
> > > > + close(fd);
> > > > +}
> > > >
> > > > int lock_contention_prepare(struct lock_contention *con)
> > > > {
> > > > @@ -109,6 +156,8 @@ int lock_contention_prepare(struct lock_contention *con)
> > > > skel->rodata->use_cgroup_v2 = 1;
> > > > }
> > > >
> > > > + check_slab_cache_iter(con);
> > > > +
> > > > if (lock_contention_bpf__load(skel) < 0) {
> > > > pr_err("Failed to load lock-contention BPF skeleton\n");
> > > > return -1;
> > > > @@ -304,6 +353,7 @@ static void account_end_timestamp(struct lock_contention *con)
> > > >
> > > > int lock_contention_start(void)
> > > > {
> > > > + run_slab_cache_iter();
> > > > skel->bss->enabled = 1;
> > > > return 0;
> > > > }
> > > > diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> > > > index 1069bda5d733887f..fd24ccb00faec0ba 100644
> > > > --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
> > > > +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> > > > @@ -100,6 +100,13 @@ struct {
> > > > __uint(max_entries, 1);
> > > > } cgroup_filter SEC(".maps");
> > > >
> > > > +struct {
> > > > + __uint(type, BPF_MAP_TYPE_HASH);
> > > > + __uint(key_size, sizeof(long));
> > > > + __uint(value_size, sizeof(struct slab_cache_data));
> > > > + __uint(max_entries, 1);
> > > > +} slab_caches SEC(".maps");
> > > > +
> > > > struct rw_semaphore___old {
> > > > struct task_struct *owner;
> > > > } __attribute__((preserve_access_index));
> > > > @@ -136,6 +143,8 @@ int perf_subsys_id = -1;
> > > >
> > > > __u64 end_ts;
> > > >
> > > > +__u32 slab_cache_id;
> > > > +
> > > > /* error stat */
> > > > int task_fail;
> > > > int stack_fail;
> > > > @@ -563,4 +572,23 @@ int BPF_PROG(end_timestamp)
> > > > return 0;
> > > > }
> > > >
> > > > +SEC("iter/kmem_cache")
> > > > +int slab_cache_iter(struct bpf_iter__kmem_cache *ctx)
> > > > +{
> > > > + struct kmem_cache *s = ctx->s;
> > > > + struct slab_cache_data d;
> > > > +
> > > > + if (s == NULL)
> > > > + return 0;
> > > > +
> > > > + d.id = ++slab_cache_id << LCB_F_SLAB_ID_SHIFT;
> > > > + bpf_probe_read_kernel_str(d.name, sizeof(d.name), s->name);
> > > > +
> > > > + if (d.id >= LCB_F_SLAB_ID_END)
> > > > + return 0;
> > > > +
> > > > + bpf_map_update_elem(&slab_caches, &s, &d, BPF_NOEXIST);
> > > > + return 0;
> > > > +}
> > > > +
> > > > char LICENSE[] SEC("license") = "Dual BSD/GPL";
> > > > diff --git a/tools/perf/util/bpf_skel/lock_data.h b/tools/perf/util/bpf_skel/lock_data.h
> > > > index 4f0aae5483745dfa..c15f734d7fc4aecb 100644
> > > > --- a/tools/perf/util/bpf_skel/lock_data.h
> > > > +++ b/tools/perf/util/bpf_skel/lock_data.h
> > > > @@ -32,9 +32,16 @@ struct contention_task_data {
> > > > #define LCD_F_MMAP_LOCK (1U << 31)
> > > > #define LCD_F_SIGHAND_LOCK (1U << 30)
> > > >
> > > > +#define LCB_F_SLAB_ID_SHIFT 16
> > > > +#define LCB_F_SLAB_ID_START (1U << 16)
> > > > +#define LCB_F_SLAB_ID_END (1U << 26)
> > > > +#define LCB_F_SLAB_ID_MASK 0x03FF0000U
> > > > +
> > > > #define LCB_F_TYPE_MAX (1U << 7)
> > > > #define LCB_F_TYPE_MASK 0x0000007FU
> > > >
> > > > +#define SLAB_NAME_MAX 28
> > > > +
> > > > struct contention_data {
> > > > u64 total_time;
> > > > u64 min_time;
> > > > @@ -55,4 +62,9 @@ enum lock_class_sym {
> > > > LOCK_CLASS_RQLOCK,
> > > > };
> > > >
> > > > +struct slab_cache_data {
> > > > + u32 id;
> > > > + char name[SLAB_NAME_MAX];
> > > > +};
> > > > +
> > > > #endif /* UTIL_BPF_SKEL_LOCK_DATA_H */
> > > > diff --git a/tools/perf/util/bpf_skel/vmlinux/vmlinux.h b/tools/perf/util/bpf_skel/vmlinux/vmlinux.h
> > > > index 4dcad7b682bdee9c..7b81d3173917fdb5 100644
> > > > --- a/tools/perf/util/bpf_skel/vmlinux/vmlinux.h
> > > > +++ b/tools/perf/util/bpf_skel/vmlinux/vmlinux.h
> > > > @@ -195,4 +195,12 @@ struct bpf_perf_event_data_kern {
> > > > */
> > > > struct rq {};
> > > >
> > > > +struct kmem_cache {
> > > > + const char *name;
> > > > +} __attribute__((preserve_access_index));
> > > > +
> > > > +struct bpf_iter__kmem_cache {
> > > > + struct kmem_cache *s;
> > > > +} __attribute__((preserve_access_index));
> > > > +
> > > > #endif // __VMLINUX_H
> > > > --
> > > > 2.47.0.277.g8800431eea-goog
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