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Message-ID: <ZvpHocNuQRBehUWp@google.com>
Date: Sun, 29 Sep 2024 23:39:29 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Howard Chu <howardchu95@...il.com>
Cc: peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
mark.rutland@....com, alexander.shishkin@...ux.intel.com,
jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
kan.liang@...ux.intel.com, linux-perf-users@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 5/8] perf record --off-cpu: Dump total off-cpu time at
the end.
On Fri, Sep 27, 2024 at 01:27:33PM -0700, Howard Chu wrote:
> By setting a placeholder sample_type and then writing real data into
> raw_data, we mimic the direct sample method to write data at the end.
>
> Note that some data serve only as placeholders and will be overwritten
> by the data in raw_data. Additionally, since the IP will be updated in
> evsel__parse_sample(), there is no need to handle it in off_cpu_write().
>
> Suggested-by: Namhyung Kim <namhyung@...nel.org>
> Signed-off-by: Howard Chu <howardchu95@...il.com>
> ---
> tools/perf/util/bpf_off_cpu.c | 116 +++++++++++++++++++++-------------
> 1 file changed, 72 insertions(+), 44 deletions(-)
>
> diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
> index f7233a09ec77..2a1cfd7e0b09 100644
> --- a/tools/perf/util/bpf_off_cpu.c
> +++ b/tools/perf/util/bpf_off_cpu.c
> @@ -138,12 +138,19 @@ int off_cpu_prepare(struct evlist *evlist, struct target *target,
> int ncpus = 1, ntasks = 1, ncgrps = 1;
> struct strlist *pid_slist = NULL;
> struct str_node *pos;
> + struct evsel *evsel;
>
> if (off_cpu_config(evlist) < 0) {
> pr_err("Failed to config off-cpu BPF event\n");
> return -1;
> }
>
> + evsel = evlist__find_evsel_by_str(evlist, OFFCPU_EVENT);
> + if (evsel == NULL) {
> + pr_err("%s evsel not found\n", OFFCPU_EVENT);
> + return -1 ;
> + }
> +
> skel = off_cpu_bpf__open();
> if (!skel) {
> pr_err("Failed to open off-cpu BPF skeleton\n");
> @@ -259,7 +266,6 @@ int off_cpu_prepare(struct evlist *evlist, struct target *target,
> }
>
> if (evlist__first(evlist)->cgrp) {
> - struct evsel *evsel;
> u8 val = 1;
>
> fd = bpf_map__fd(skel->maps.cgroup_filter);
> @@ -280,6 +286,7 @@ int off_cpu_prepare(struct evlist *evlist, struct target *target,
> }
> }
>
> + skel->bss->sample_type = OFFCPU_EMBEDDED_SAMPLE_TYPES;
Hmm.. you set the sample_type unconditionally which means the embedded
data in the raw area has the fixed format. Then I think you don't need
the sample_type variable at all.
> skel->bss->offcpu_thresh = opts->off_cpu_thresh * 1000;
>
> err = off_cpu_bpf__attach(skel);
> @@ -305,7 +312,8 @@ int off_cpu_write(struct perf_session *session)
> {
> int bytes = 0, size;
> int fd, stack;
> - u64 sample_type, val, sid = 0;
> + u32 raw_size;
> + u64 sample_type_off_cpu, sample_type_bpf_output, val, sid = 0, tstamp = OFF_CPU_TIMESTAMP;
> struct evsel *evsel;
> struct perf_data_file *file = &session->data->file;
> struct off_cpu_key prev, key;
> @@ -315,7 +323,6 @@ int off_cpu_write(struct perf_session *session)
> .misc = PERF_RECORD_MISC_USER,
> },
> };
> - u64 tstamp = OFF_CPU_TIMESTAMP;
>
> skel->bss->enabled = 0;
>
> @@ -325,15 +332,10 @@ int off_cpu_write(struct perf_session *session)
> return 0;
> }
>
> - sample_type = evsel->core.attr.sample_type;
> -
> - if (sample_type & ~OFFCPU_SAMPLE_TYPES) {
> - pr_err("not supported sample type: %llx\n",
> - (unsigned long long)sample_type);
> - return -1;
> - }
> + sample_type_off_cpu = OFFCPU_EMBEDDED_SAMPLE_TYPES;
> + sample_type_bpf_output = evsel->core.attr.sample_type;
>
> - if (sample_type & (PERF_SAMPLE_ID | PERF_SAMPLE_IDENTIFIER)) {
> + if (sample_type_bpf_output & (PERF_SAMPLE_ID | PERF_SAMPLE_IDENTIFIER)) {
> if (evsel->core.id)
> sid = evsel->core.id[0];
> }
> @@ -344,49 +346,75 @@ int off_cpu_write(struct perf_session *session)
>
> while (!bpf_map_get_next_key(fd, &prev, &key)) {
> int n = 1; /* start from perf_event_header */
> - int ip_pos = -1;
> + int i = 0; /* raw data index */
>
> bpf_map_lookup_elem(fd, &key, &val);
>
> - if (sample_type & PERF_SAMPLE_IDENTIFIER)
> + /*
> + * Zero-fill some of these fields first, they will be overwritten by the dummy
> + * embedded data (in raw_data) below, when parsing the samples. And because embedded
> + * data is in BPF output, perf script -F without bpf-output field will not work
> + * properly.
> + */
> + if (sample_type_bpf_output & PERF_SAMPLE_IDENTIFIER)
> data.array[n++] = sid;
> - if (sample_type & PERF_SAMPLE_IP) {
> - ip_pos = n;
> - data.array[n++] = 0; /* will be updated */
> - }
> - if (sample_type & PERF_SAMPLE_TID)
> - data.array[n++] = (u64)key.pid << 32 | key.tgid;
> - if (sample_type & PERF_SAMPLE_TIME)
> - data.array[n++] = tstamp;
> - if (sample_type & PERF_SAMPLE_ID)
> - data.array[n++] = sid;
> - if (sample_type & PERF_SAMPLE_CPU)
> + if (sample_type_bpf_output & PERF_SAMPLE_IP)
> data.array[n++] = 0;
> - if (sample_type & PERF_SAMPLE_PERIOD)
> - data.array[n++] = val;
> - if (sample_type & PERF_SAMPLE_CALLCHAIN) {
> - int len = 0;
> -
> - /* data.array[n] is callchain->nr (updated later) */
> - data.array[n + 1] = PERF_CONTEXT_USER;
> - data.array[n + 2] = 0;
> + if (sample_type_bpf_output & PERF_SAMPLE_TID)
> + data.array[n++] = 0;
I'm not sure if it works correctly. You haven't set the callchain
length and 'n' is not updated.
> + if (sample_type_bpf_output & PERF_SAMPLE_TIME)
> + data.array[n++] = tstamp; /* we won't overwrite time */
> + if (sample_type_bpf_output & PERF_SAMPLE_CPU)
> + data.array[n++] = 0;
> + if (sample_type_bpf_output & PERF_SAMPLE_PERIOD)
> + data.array[n++] = 0;
> + if (sample_type_bpf_output & PERF_SAMPLE_RAW) {
> + /*
> + * the format of raw data is as follows:
> + *
> + * [ size ][ data ]
> + * [ data ]
> + * [ data ]
> + * [ data ]
> + * [ data ][ empty]
> + *
> + */
> + if (sample_type_off_cpu & PERF_SAMPLE_TID)
As I said, you can get rid of the sample_type_off_cpu check if it's
always true.
Thanks,
Namhyung
> + off_cpu_raw_data[i++] = (u64)key.pid << 32 | key.tgid;
> + if (sample_type_off_cpu & PERF_SAMPLE_PERIOD)
> + off_cpu_raw_data[i++] = val;
> + if (sample_type_off_cpu & PERF_SAMPLE_CALLCHAIN) {
> + int len = 0;
> +
> + /* off_cpu_raw_data[n] is callchain->nr (updated later) */
> + off_cpu_raw_data[i + 1] = PERF_CONTEXT_USER;
> + off_cpu_raw_data[i + 2] = 0;
> +
> + bpf_map_lookup_elem(stack, &key.stack_id, &off_cpu_raw_data[i + 2]);
> + while (off_cpu_raw_data[i + 2 + len])
> + len++;
> +
> + /* update length of callchain */
> + off_cpu_raw_data[i] = len + 1;
> +
> + /* calculate sample callchain off_cpu_raw_data length */
> + i += len + 2;
> + }
> + if (sample_type_off_cpu & PERF_SAMPLE_CGROUP)
> + off_cpu_raw_data[i++] = key.cgroup_id;
>
> - bpf_map_lookup_elem(stack, &key.stack_id, &data.array[n + 2]);
> - while (data.array[n + 2 + len])
> - len++;
> + raw_size = i * sizeof(u64) + sizeof(u32); /* 4 empty bytes for alignment */
>
> - /* update length of callchain */
> - data.array[n] = len + 1;
> + /* raw_size */
> + memcpy((void *)data.array + n * sizeof(u64), &raw_size, sizeof(raw_size));
>
> - /* update sample ip with the first callchain entry */
> - if (ip_pos >= 0)
> - data.array[ip_pos] = data.array[n + 2];
> + /* raw_data */
> + memcpy((void *)data.array + n * sizeof(u64) + sizeof(u32), off_cpu_raw_data, i * sizeof(u64));
>
> - /* calculate sample callchain data array length */
> - n += len + 2;
> + n += i + 1;
> }
> - if (sample_type & PERF_SAMPLE_CGROUP)
> - data.array[n++] = key.cgroup_id;
> + if (sample_type_bpf_output & PERF_SAMPLE_CGROUP)
> + data.array[n++] = 0;
>
> size = n * sizeof(u64);
> data.hdr.size = size;
> --
> 2.43.0
>
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