On Mon, Aug 05, 2024 at 12:03:14PM -0300, Arnaldo Carvalho de Melo wrote:
> On Fri, Aug 02, 2024 at 10:37:52AM -0700, Namhyung Kim wrote:
> > So far it used tgid as a key to get the filter expressions in the
> > pinned filters map for regular users but it won't work well if the has
> > more than one filters at the same time. Let's add the event id to the
> > key of the filter hash map so that it can identify the right filter
> > expression in the BPF program.
> >
> > As the event can be inherited to child tasks, it should use the primary
> > id which belongs to the parent (original) event. Since evsel opens the
> > event for multiple CPUs and tasks, it needs to maintain a separate hash
> > map for the event id.
>
> I'm trying to test it now, it would be nice to have the series of events
> needed to test that the feature is working.
Sure, I used the following command.
./perf record -e cycles --filter 'ip < 0xffffffff00000000' -e instructions --filter 'period < 100000' -o- ./perf test -w noploop | ./perf script -i-
>
> Some comments below.
>
> > In the user space, it keeps a list for the multiple evsel and release
> > the entries in the both hash map when it closes the event.
> >
> > Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> > ---
> > tools/perf/util/bpf-filter.c | 288 ++++++++++++++++---
> > tools/perf/util/bpf_skel/sample-filter.h | 11 +-
> > tools/perf/util/bpf_skel/sample_filter.bpf.c | 42 ++-
> > tools/perf/util/bpf_skel/vmlinux/vmlinux.h | 5 +
> > 4 files changed, 304 insertions(+), 42 deletions(-)
> >
> > diff --git a/tools/perf/util/bpf-filter.c b/tools/perf/util/bpf-filter.c
> > index c5eb0b7eec19..69b147cba969 100644
> > --- a/tools/perf/util/bpf-filter.c
> > +++ b/tools/perf/util/bpf-filter.c
> > @@ -1,4 +1,45 @@
> > /* SPDX-License-Identifier: GPL-2.0 */
> > +/**
> > + * Generic event filter for sampling events in BPF.
> > + *
> > + * The BPF program is fixed and just to read filter expressions in the 'filters'
> > + * map and compare the sample data in order to reject samples that don't match.
> > + * Each filter expression contains a sample flag (term) to compare, an operation
> > + * (==, >=, and so on) and a value.
> > + *
> > + * Note that each entry has an array of filter repxressions and it only succeeds
>
> expressions
Oops, thanks.
>
> > + * when all of the expressions are satisfied. But it supports the logical OR
> > + * using a GROUP operation which is satisfied when any of its member expression
> > + * is evaluated to true. But it doesn't allow nested GROUP operations for now.
> > + *
> > + * To support non-root users, the filters map can be loaded and pinned in the BPF
> > + * filesystem by root (perf record --setup-filter pin). Then each user will get
> > + * a new entry in the shared filters map to fill the filter expressions. And the
> > + * BPF program will find the filter using (task-id, event-id) as a key.
> > + *
> > + * The pinned BPF object (shared for regular users) has:
> > + *
> > + * event_hash |
> > + * | | |
> > + * event->id ---> | id | ---+ idx_hash | filters
> > + * | | | | | | | |
> > + * | .... | +-> | idx | --+--> | exprs | ---> perf_bpf_filter_entry[]
> > + * | | | | | | .op
> > + * task id (tgid) --------------+ | .... | | | ... | .term (+ part)
> > + * | .value
> > + * |
> > + * ======= (root would skip this part) ======== (compares it in a loop)
> > + *
> > + * This is used for per-task use cases while system-wide profiling (normally from
> > + * root user) uses a separate copy of the program and the maps for its own so that
> > + * it can proceed even if a lot of non-root users are using the filters at the
> > + * same time. In this case the filters map has a single entry and no need to use
> > + * the hash maps to get the index (key) of the filters map (IOW it's always 0).
> > + *
> > + * The BPF program returns 1 to accept the sample or 0 to drop it.
> > + * The 'dropped' map is to keep how many samples it dropped by the filter and
> > + * it will be reported as lost samples.
>
> I think there is value in reporting how many were filtered out, I'm just
> unsure about reporting it as "lost" samples, as lost has another
> semantic associated, i.e. ring buffer was full or couldn't process it
> for some other resource starvation issue, no?
Then we need a way to save the information. It could be a new record
type (PERF_RECORD_DROPPED_SAMPLES), a new misc flag in the lost samples
record or a header field. I prefer the misc flag.
Also there should be a separate PERF_RECORD_LOST record in the middle
when there's actual issue. Without that we can say it's from the BPF.
Thanks,
Namhyung
>
> > + */
> > #include <stdlib.h>
> > #include <fcntl.h>
> > #include <sys/ioctl.h>
> > @@ -6,6 +47,7 @@
> >
> > #include <bpf/bpf.h>
> > #include <linux/err.h>
> > +#include <linux/list.h>
> > #include <api/fs/fs.h>
> > #include <internal/xyarray.h>
> > #include <perf/threadmap.h>
> > @@ -27,7 +69,14 @@
> > #define PERF_SAMPLE_TYPE(_st, opt) __PERF_SAMPLE_TYPE(PBF_TERM_##_st, PERF_SAMPLE_##_st, opt)
> >
> > /* Index in the pinned 'filters' map. Should be released after use. */
> > -static int pinned_filter_idx = -1;
> > +struct pinned_filter_idx {
> > + struct list_head list;
> > + struct evsel *evsel;
> > + u64 event_id;
> > + int hash_idx;
> > +};
> > +
> > +static LIST_HEAD(pinned_filters);
> >
> > static const struct perf_sample_info {
> > enum perf_bpf_filter_term type;
> > @@ -175,24 +224,145 @@ static int convert_to_tgid(int tid)
> > return tgid;
> > }
> >
> > -static int update_pid_hash(struct evsel *evsel, struct perf_bpf_filter_entry *entry)
> > +/*
> > + * The event might be closed already so we cannot get the list of ids using FD
> > + * like in create_event_hash() below, let's iterate the event_hash map and
> > + * delete all entries that have the event id as a key.
> > + */
> > +static void destroy_event_hash(u64 event_id)
> > +{
> > + int fd;
> > + u64 key, *prev_key = NULL;
> > + int num = 0, alloced = 32;
> > + u64 *ids = calloc(alloced, sizeof(*ids));
> > +
> > + if (ids == NULL)
> > + return;
> > +
> > + fd = get_pinned_fd("event_hash");
> > + if (fd < 0) {
> > + pr_debug("cannot get fd for 'event_hash' map\n");
> > + free(ids);
> > + return;
> > + }
> > +
> > + /* Iterate the whole map to collect keys for the event id. */
> > + while (!bpf_map_get_next_key(fd, prev_key, &key)) {
> > + u64 id;
> > +
> > + if (bpf_map_lookup_elem(fd, &key, &id) == 0 && id == event_id) {
> > + if (num == alloced) {
> > + void *tmp;
> > +
> > + alloced *= 2;
> > + tmp = realloc(ids, alloced * sizeof(*ids));
> > + if (tmp == NULL)
> > + break;
> > +
> > + ids = tmp;
> > + }
> > + ids[num++] = key;
> > + }
> > +
> > + prev_key = &key;
> > + }
> > +
> > + for (int i = 0; i < num; i++)
> > + bpf_map_delete_elem(fd, &ids[i]);
> > +
> > + free(ids);
> > + close(fd);
> > +}
> > +
> > +/*
> > + * Return a representative id if ok, or 0 for failures.
> > + *
> > + * The perf_event->id is good for this, but an evsel would have multiple
> > + * instances for CPUs and tasks. So pick up the first id and setup a hash
> > + * from id of each instance to the representative id (the first one).
> > + */
> > +static u64 create_event_hash(struct evsel *evsel)
> > +{
> > + int x, y, fd;
> > + u64 the_id = 0, id;
> > +
> > + fd = get_pinned_fd("event_hash");
> > + if (fd < 0) {
> > + pr_err("cannot get fd for 'event_hash' map\n");
> > + return 0;
> > + }
> > +
> > + for (x = 0; x < xyarray__max_x(evsel->core.fd); x++) {
> > + for (y = 0; y < xyarray__max_y(evsel->core.fd); y++) {
> > + int ret = ioctl(FD(evsel, x, y), PERF_EVENT_IOC_ID, &id);
> > +
> > + if (ret < 0) {
> > + pr_err("Failed to get the event id\n");
> > + if (the_id)
> > + destroy_event_hash(the_id);
> > + return 0;
> > + }
> > +
> > + if (the_id == 0)
> > + the_id = id;
> > +
> > + bpf_map_update_elem(fd, &id, &the_id, BPF_ANY);
> > + }
> > + }
> > +
> > + close(fd);
> > + return the_id;
> > +}
> > +
> > +static void destroy_idx_hash(struct pinned_filter_idx *pfi)
> > +{
> > + int fd, nr;
> > + struct perf_thread_map *threads;
> > +
> > + fd = get_pinned_fd("filters");
> > + bpf_map_delete_elem(fd, &pfi->hash_idx);
> > + close(fd);
> > +
> > + if (pfi->event_id)
> > + destroy_event_hash(pfi->event_id);
> > +
> > + threads = perf_evsel__threads(&pfi->evsel->core);
> > + if (threads == NULL)
> > + return;
> > +
> > + fd = get_pinned_fd("idx_hash");
> > + nr = perf_thread_map__nr(threads);
> > + for (int i = 0; i < nr; i++) {
> > + /* The target task might be dead already, just try the pid */
> > + struct idx_hash_key key = {
> > + .evt_id = pfi->event_id,
> > + .tgid = perf_thread_map__pid(threads, i),
> > + };
> > +
> > + bpf_map_delete_elem(fd, &key);
> > + }
> > + close(fd);
> > +}
> > +
> > +/* Maintain a hashmap from (tgid, event-id) to filter index */
> > +static int create_idx_hash(struct evsel *evsel, struct perf_bpf_filter_entry *entry)
> > {
> > int filter_idx;
> > int fd, nr, last;
> > + u64 event_id = 0;
> > + struct pinned_filter_idx *pfi = NULL;
> > struct perf_thread_map *threads;
> >
> > fd = get_pinned_fd("filters");
> > if (fd < 0) {
> > - pr_debug("cannot get fd for 'filters' map\n");
> > + pr_err("cannot get fd for 'filters' map\n");
> > return fd;
> > }
> >
> > /* Find the first available entry in the filters map */
> > for (filter_idx = 0; filter_idx < MAX_FILTERS; filter_idx++) {
> > - if (bpf_map_update_elem(fd, &filter_idx, entry, BPF_NOEXIST) == 0) {
> > - pinned_filter_idx = filter_idx;
> > + if (bpf_map_update_elem(fd, &filter_idx, entry, BPF_NOEXIST) == 0)
> > break;
> > - }
> > }
> > close(fd);
> >
> > @@ -201,22 +371,44 @@ static int update_pid_hash(struct evsel *evsel, struct perf_bpf_filter_entry *en
> > return -EBUSY;
> > }
> >
> > + pfi = zalloc(sizeof(*pfi));
> > + if (pfi == NULL) {
> > + pr_err("Cannot save pinned filter index\n");
> > + goto err;
> > + }
> > +
> > + pfi->evsel = evsel;
> > + pfi->hash_idx = filter_idx;
> > +
> > + event_id = create_event_hash(evsel);
> > + if (event_id == 0) {
> > + pr_err("Cannot update the event hash\n");
> > + goto err;
> > + }
> > +
> > + pfi->event_id = event_id;
> > +
> > threads = perf_evsel__threads(&evsel->core);
> > if (threads == NULL) {
> > pr_err("Cannot get the thread list of the event\n");
> > - return -EINVAL;
> > + goto err;
> > }
> >
> > /* save the index to a hash map */
> > - fd = get_pinned_fd("pid_hash");
> > - if (fd < 0)
> > - return fd;
> > + fd = get_pinned_fd("idx_hash");
> > + if (fd < 0) {
> > + pr_err("cannot get fd for 'idx_hash' map\n");
> > + goto err;
> > + }
> >
> > last = -1;
> > nr = perf_thread_map__nr(threads);
> > for (int i = 0; i < nr; i++) {
> > int pid = perf_thread_map__pid(threads, i);
> > int tgid;
> > + struct idx_hash_key key = {
> > + .evt_id = event_id,
> > + };
> >
> > /* it actually needs tgid, let's get tgid from /proc. */
> > tgid = convert_to_tgid(pid);
> > @@ -228,16 +420,25 @@ static int update_pid_hash(struct evsel *evsel, struct perf_bpf_filter_entry *en
> > if (tgid == last)
> > continue;
> > last = tgid;
> > + key.tgid = tgid;
> >
> > - if (bpf_map_update_elem(fd, &tgid, &filter_idx, BPF_ANY) < 0) {
> > - pr_err("Failed to update the pid hash\n");
> > + if (bpf_map_update_elem(fd, &key, &filter_idx, BPF_ANY) < 0) {
> > + pr_err("Failed to update the idx_hash\n");
> > close(fd);
> > - return -1;
> > + goto err;
> > }
> > - pr_debug("pid hash: %d -> %d\n", tgid, filter_idx);
> > + pr_debug("bpf-filter: idx_hash (task=%d,%s) -> %d\n",
> > + tgid, evsel__name(evsel), filter_idx);
> > }
> > +
> > + list_add(&pfi->list, &pinned_filters);
> > close(fd);
> > - return 0;
> > + return filter_idx;
> > +
> > +err:
> > + destroy_idx_hash(pfi);
> > + free(pfi);
> > + return -1;
> > }
> >
> > int perf_bpf_filter__prepare(struct evsel *evsel, struct target *target)
> > @@ -247,7 +448,7 @@ int perf_bpf_filter__prepare(struct evsel *evsel, struct target *target)
> > struct bpf_program *prog;
> > struct bpf_link *link;
> > struct perf_bpf_filter_entry *entry;
> > - bool needs_pid_hash = !target__has_cpu(target) && !target->uid_str;
> > + bool needs_idx_hash = !target__has_cpu(target) && !target->uid_str;
> >
> > entry = calloc(MAX_FILTERS, sizeof(*entry));
> > if (entry == NULL)
> > @@ -259,11 +460,11 @@ int perf_bpf_filter__prepare(struct evsel *evsel, struct target *target)
> > goto err;
> > }
> >
> > - if (needs_pid_hash && geteuid() != 0) {
> > + if (needs_idx_hash && geteuid() != 0) {
> > int zero = 0;
> >
> > /* The filters map is shared among other processes */
> > - ret = update_pid_hash(evsel, entry);
> > + ret = create_idx_hash(evsel, entry);
> > if (ret < 0)
> > goto err;
> >
> > @@ -274,7 +475,7 @@ int perf_bpf_filter__prepare(struct evsel *evsel, struct target *target)
> > }
> >
> > /* Reset the lost count */
> > - bpf_map_update_elem(fd, &pinned_filter_idx, &zero, BPF_ANY);
> > + bpf_map_update_elem(fd, &ret, &zero, BPF_ANY);
> > close(fd);
> >
> > fd = get_pinned_fd("perf_sample_filter");
> > @@ -288,6 +489,7 @@ int perf_bpf_filter__prepare(struct evsel *evsel, struct target *target)
> > ret = ioctl(FD(evsel, x, y), PERF_EVENT_IOC_SET_BPF, fd);
> > if (ret < 0) {
> > pr_err("Failed to attach perf sample-filter\n");
> > + close(fd);
> > goto err;
> > }
> > }
> > @@ -332,6 +534,15 @@ int perf_bpf_filter__prepare(struct evsel *evsel, struct target *target)
> >
> > err:
> > free(entry);
> > + if (!list_empty(&pinned_filters)) {
> > + struct pinned_filter_idx *pfi, *tmp;
> > +
> > + list_for_each_entry_safe(pfi, tmp, &pinned_filters, list) {
> > + destroy_idx_hash(pfi);
> > + list_del(&pfi->list);
>
> list_del_init()? But I see you're not using it
> in other places,like in perf_bpf_filter__destroy().
>
> > + free(pfi);
> > + }
> > + }
> > sample_filter_bpf__destroy(skel);
> > return ret;
> > }
> > @@ -339,6 +550,7 @@ int perf_bpf_filter__prepare(struct evsel *evsel, struct target *target)
> > int perf_bpf_filter__destroy(struct evsel *evsel)
> > {
> > struct perf_bpf_filter_expr *expr, *tmp;
> > + struct pinned_filter_idx *pfi, *pos;
> >
> > list_for_each_entry_safe(expr, tmp, &evsel->bpf_filters, list) {
> > list_del(&expr->list);
> > @@ -346,14 +558,11 @@ int perf_bpf_filter__destroy(struct evsel *evsel)
> > }
> > sample_filter_bpf__destroy(evsel->bpf_skel);
> >
> > - if (pinned_filter_idx >= 0) {
> > - int fd = get_pinned_fd("filters");
> > -
> > - bpf_map_delete_elem(fd, &pinned_filter_idx);
> > - pinned_filter_idx = -1;
> > - close(fd);
> > + list_for_each_entry_safe(pfi, pos, &pinned_filters, list) {
> > + destroy_idx_hash(pfi);
> > + list_del(&pfi->list);
> > + free(pfi);
> > }
> > -
> > return 0;
> > }
> >
> > @@ -364,10 +573,20 @@ u64 perf_bpf_filter__lost_count(struct evsel *evsel)
> > if (list_empty(&evsel->bpf_filters))
> > return 0;
> >
> > - if (pinned_filter_idx >= 0) {
> > + if (!list_empty(&pinned_filters)) {
> > int fd = get_pinned_fd("dropped");
> > + struct pinned_filter_idx *pfi;
> > +
> > + if (fd < 0)
> > + return 0;
> >
> > - bpf_map_lookup_elem(fd, &pinned_filter_idx, &count);
> > + list_for_each_entry(pfi, &pinned_filters, list) {
> > + if (pfi->evsel != evsel)
> > + continue;
> > +
> > + bpf_map_lookup_elem(fd, &pfi->hash_idx, &count);
> > + break;
> > + }
> > close(fd);
> > } else if (evsel->bpf_skel) {
> > struct sample_filter_bpf *skel = evsel->bpf_skel;
> > @@ -429,9 +648,10 @@ int perf_bpf_filter__pin(void)
> >
> > /* pinned program will use pid-hash */
> > bpf_map__set_max_entries(skel->maps.filters, MAX_FILTERS);
> > - bpf_map__set_max_entries(skel->maps.pid_hash, MAX_PIDS);
> > + bpf_map__set_max_entries(skel->maps.event_hash, MAX_EVT_HASH);
> > + bpf_map__set_max_entries(skel->maps.idx_hash, MAX_IDX_HASH);
> > bpf_map__set_max_entries(skel->maps.dropped, MAX_FILTERS);
> > - skel->rodata->use_pid_hash = 1;
> > + skel->rodata->use_idx_hash = 1;
> >
> > if (sample_filter_bpf__load(skel) < 0) {
> > ret = -errno;
> > @@ -484,8 +704,12 @@ int perf_bpf_filter__pin(void)
> > pr_debug("chmod for filters failed\n");
> > ret = -errno;
> > }
> > - if (fchmodat(dir_fd, "pid_hash", 0666, 0) < 0) {
> > - pr_debug("chmod for pid_hash failed\n");
> > + if (fchmodat(dir_fd, "event_hash", 0666, 0) < 0) {
> > + pr_debug("chmod for event_hash failed\n");
> > + ret = -errno;
> > + }
> > + if (fchmodat(dir_fd, "idx_hash", 0666, 0) < 0) {
> > + pr_debug("chmod for idx_hash failed\n");
> > ret = -errno;
> > }
> > if (fchmodat(dir_fd, "dropped", 0666, 0) < 0) {
> > diff --git a/tools/perf/util/bpf_skel/sample-filter.h b/tools/perf/util/bpf_skel/sample-filter.h
> > index e666bfd5fbdd..5f0c8e4e83d3 100644
> > --- a/tools/perf/util/bpf_skel/sample-filter.h
> > +++ b/tools/perf/util/bpf_skel/sample-filter.h
> > @@ -1,8 +1,9 @@
> > #ifndef PERF_UTIL_BPF_SKEL_SAMPLE_FILTER_H
> > #define PERF_UTIL_BPF_SKEL_SAMPLE_FILTER_H
> >
> > -#define MAX_FILTERS 64
> > -#define MAX_PIDS (16 * 1024)
> > +#define MAX_FILTERS 64
> > +#define MAX_IDX_HASH (16 * 1024)
> > +#define MAX_EVT_HASH (1024 * 1024)
> >
> > /* supported filter operations */
> > enum perf_bpf_filter_op {
> > @@ -62,4 +63,10 @@ struct perf_bpf_filter_entry {
> > __u64 value;
> > };
> >
> > +struct idx_hash_key {
> > + __u64 evt_id;
> > + __u32 tgid;
> > + __u32 reserved;
> > +};
> > +
> > #endif /* PERF_UTIL_BPF_SKEL_SAMPLE_FILTER_H */
> > diff --git a/tools/perf/util/bpf_skel/sample_filter.bpf.c b/tools/perf/util/bpf_skel/sample_filter.bpf.c
> > index 4c75354b84fd..4872a16eedfd 100644
> > --- a/tools/perf/util/bpf_skel/sample_filter.bpf.c
> > +++ b/tools/perf/util/bpf_skel/sample_filter.bpf.c
> > @@ -15,13 +15,25 @@ struct filters {
> > __uint(max_entries, 1);
> > } filters SEC(".maps");
> >
> > -/* tgid to filter index */
> > -struct pid_hash {
> > +/*
> > + * An evsel has multiple instances for each CPU or task but we need a single
> > + * id to be used as a key for the idx_hash. This hashmap would translate the
> > + * instance's ID to a representative ID.
> > + */
> > +struct event_hash {
> > __uint(type, BPF_MAP_TYPE_HASH);
> > - __type(key, int);
> > + __type(key, __u64);
> > + __type(value, __u64);
> > + __uint(max_entries, 1);
> > +} event_hash SEC(".maps");
> > +
> > +/* tgid/evtid to filter index */
> > +struct idx_hash {
> > + __uint(type, BPF_MAP_TYPE_HASH);
> > + __type(key, struct idx_hash_key);
> > __type(value, int);
> > __uint(max_entries, 1);
> > -} pid_hash SEC(".maps");
> > +} idx_hash SEC(".maps");
> >
> > /* tgid to filter index */
> > struct lost_count {
> > @@ -31,7 +43,7 @@ struct lost_count {
> > __uint(max_entries, 1);
> > } dropped SEC(".maps");
> >
> > -volatile const int use_pid_hash;
> > +volatile const int use_idx_hash;
> >
> > void *bpf_cast_to_kern_ctx(void *) __ksym;
> >
> > @@ -202,11 +214,25 @@ int perf_sample_filter(void *ctx)
> >
> > k = 0;
> >
> > - if (use_pid_hash) {
> > - int tgid = bpf_get_current_pid_tgid() >> 32;
> > + if (use_idx_hash) {
> > + struct idx_hash_key key = {
> > + .tgid = bpf_get_current_pid_tgid() >> 32,
> > + };
> > + __u64 eid = kctx->event->id;
> > + __u64 *key_id;
> > int *idx;
> >
> > - idx = bpf_map_lookup_elem(&pid_hash, &tgid);
> > + /* get primary_event_id */
> > + if (kctx->event->parent)
> > + eid = kctx->event->parent->id;
> > +
> > + key_id = bpf_map_lookup_elem(&event_hash, &eid);
> > + if (key_id == NULL)
> > + goto drop;
> > +
> > + key.evt_id = *key_id;
> > +
> > + idx = bpf_map_lookup_elem(&idx_hash, &key);
> > if (idx)
> > k = *idx;
> > else
> > diff --git a/tools/perf/util/bpf_skel/vmlinux/vmlinux.h b/tools/perf/util/bpf_skel/vmlinux/vmlinux.h
> > index e9028235d771..05edc7d28151 100644
> > --- a/tools/perf/util/bpf_skel/vmlinux/vmlinux.h
> > +++ b/tools/perf/util/bpf_skel/vmlinux/vmlinux.h
> > @@ -174,6 +174,11 @@ struct perf_sample_data {
> > u64 code_page_size;
> > } __attribute__((__aligned__(64))) __attribute__((preserve_access_index));
> >
> > +struct perf_event {
> > + struct perf_event *parent;
> > + u64 id;
> > +} __attribute__((preserve_access_index));
> > +
> > struct bpf_perf_event_data_kern {
> > struct perf_sample_data *data;
> > struct perf_event *event;
> > --
> > 2.46.0.rc2.264.g509ed76dc8-goog
