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libbpf: Don't attach perf_buffer to offline/missing CPUs

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It's quite common on some systems to have more CPUs enlisted as "possible",
than there are (and could ever be) present/online CPUs. In such cases,
perf_buffer creationg will fail due to inability to create perf event on
missing CPU with error like this:

libbpf: failed to open perf buffer event on cpu #16: No such device

This patch fixes the logic of perf_buffer__new() to ignore CPUs that are
missing or currently offline. In rare cases where user explicitly listed
specific CPUs to connect to, behavior is unchanged: libbpf will try to open
perf event buffer on specified CPU(s) anyways.

Fixes: fb84b82246 ("libbpf: add perf buffer API")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191212013609.1691168-1-andriin@fb.com
This commit is contained in:
Andrii Nakryiko 2019-12-11 17:36:09 -08:00 committed by Alexei Starovoitov
parent 65bc4c4063
commit 783b8f01f5
1 changed files with 25 additions and 7 deletions
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32
tools/lib/bpf/libbpf.c
View File

@ -5946,7 +5946,7 @@ struct perf_buffer {
size_t mmap_size;
struct perf_cpu_buf **cpu_bufs;
struct epoll_event *events;
int cpu_cnt;
int cpu_cnt; /* number of allocated CPU buffers */
int epoll_fd; /* perf event FD */
int map_fd; /* BPF_MAP_TYPE_PERF_EVENT_ARRAY BPF map FD */
};
@ -6080,11 +6080,13 @@ perf_buffer__new_raw(int map_fd, size_t page_cnt,
static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt,
struct perf_buffer_params *p)
{
const char *online_cpus_file = "/sys/devices/system/cpu/online";
struct bpf_map_info map = {};
char msg[STRERR_BUFSIZE];
struct perf_buffer *pb;
bool *online = NULL;
__u32 map_info_len;
int err, i;
int err, i, j, n;
if (page_cnt & (page_cnt - 1)) {
pr_warn("page count should be power of two, but is %zu\n",
@ -6153,20 +6155,32 @@ static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt,
goto error;
}
for (i = 0; i < pb->cpu_cnt; i++) {
err = parse_cpu_mask_file(online_cpus_file, &online, &n);
if (err) {
pr_warn("failed to get online CPU mask: %d\n", err);
goto error;
}
for (i = 0, j = 0; i < pb->cpu_cnt; i++) {
struct perf_cpu_buf *cpu_buf;
int cpu, map_key;
cpu = p->cpu_cnt > 0 ? p->cpus[i] : i;
map_key = p->cpu_cnt > 0 ? p->map_keys[i] : i;
/* in case user didn't explicitly requested particular CPUs to
* be attached to, skip offline/not present CPUs
*/
if (p->cpu_cnt <= 0 && (cpu >= n || !online[cpu]))
continue;
cpu_buf = perf_buffer__open_cpu_buf(pb, p->attr, cpu, map_key);
if (IS_ERR(cpu_buf)) {
err = PTR_ERR(cpu_buf);
goto error;
}
pb->cpu_bufs[i] = cpu_buf;
pb->cpu_bufs[j] = cpu_buf;
err = bpf_map_update_elem(pb->map_fd, &map_key,
&cpu_buf->fd, 0);
@ -6178,21 +6192,25 @@ static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt,
goto error;
}
pb->events[i].events = EPOLLIN;
pb->events[i].data.ptr = cpu_buf;
pb->events[j].events = EPOLLIN;
pb->events[j].data.ptr = cpu_buf;
if (epoll_ctl(pb->epoll_fd, EPOLL_CTL_ADD, cpu_buf->fd,
&pb->events[i]) < 0) {
&pb->events[j]) < 0) {
err = -errno;
pr_warn("failed to epoll_ctl cpu #%d perf FD %d: %s\n",
cpu, cpu_buf->fd,
libbpf_strerror_r(err, msg, sizeof(msg)));
goto error;
}
j++;
}
pb->cpu_cnt = j;
free(online);
return pb;
error:
free(online);
if (pb)
perf_buffer__free(pb);
return ERR_PTR(err);