Re: [PATCH v3 20/50] perf record: Be lazier in allocating lost samples buffer

[Yang Jihong]

Hello,

On 2023/10/25 6:23, Ian Rogers wrote:
> Wait until a lost sample occurs to allocate the lost samples buffer,
> often the buffer isn't necessary. This saves a 64kb allocation and
> 5.3kb of peak memory consumption.
>
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
>   tools/perf/builtin-record.c | 29 +++++++++++++++++++----------
>   1 file changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 9b4f3805ca92..b6c8c1371b39 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -1924,21 +1924,13 @@ static void __record__save_lost_samples(struct record *rec, struct evsel *evsel,
>   static void record__read_lost_samples(struct record *rec)
>   {
>   	struct perf_session *session = rec->session;
> -	struct perf_record_lost_samples *lost;
> +	struct perf_record_lost_samples *lost = NULL;
>   	struct evsel *evsel;
>   
>   	/* there was an error during record__open */
>   	if (session->evlist == NULL)
>   		return;
>   
> -	lost = zalloc(PERF_SAMPLE_MAX_SIZE);
> -	if (lost == NULL) {
> -		pr_debug("Memory allocation failed\n");
> -		return;
> -	}
> -
> -	lost->header.type = PERF_RECORD_LOST_SAMPLES;
> -
>   	evlist__for_each_entry(session->evlist, evsel) {
>   		struct xyarray *xy = evsel->core.sample_id;
>   		u64 lost_count;
> @@ -1961,6 +1953,14 @@ static void record__read_lost_samples(struct record *rec)
>   				}
>   
>   				if (count.lost) {
> +					if (!lost) {
> +						lost = zalloc(PERF_SAMPLE_MAX_SIZE);
> +						if (!lost) {
> +							pr_debug("Memory allocation failed\n");
> +							return;
> +						}
> +						lost->header.type = PERF_RECORD_LOST_SAMPLES;
> +					}
>   					__record__save_lost_samples(rec, evsel, lost,
>   								    x, y, count.lost, 0);
>   				}
> @@ -1968,9 +1968,18 @@ static void record__read_lost_samples(struct record *rec)
>   		}
>   
>   		lost_count = perf_bpf_filter__lost_count(evsel);
> -		if (lost_count)
> +		if (lost_count) {
> +			if (!lost) {
> +				lost = zalloc(PERF_SAMPLE_MAX_SIZE);
> +				if (!lost) {
> +					pr_debug("Memory allocation failed\n");
> +					return;
> +				}
> +				lost->header.type = PERF_RECORD_LOST_SAMPLES;
> +			}
>   			__record__save_lost_samples(rec, evsel, lost, 0, 0, lost_count,
>   						    PERF_RECORD_MISC_LOST_SAMPLES_BPF);
> +		}
>   	}

Can zalloc for `lost` be moved to __record__save_lost_samples?
This simplifies the code.


diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index dcf288a4fb9a..8d2eb746031a 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1888,14 +1888,25 @@ record__switch_output(struct record *rec, bool 
at_exit)
 }

 static void __record__save_lost_samples(struct record *rec, struct 
evsel *evsel,
-                                       struct perf_record_lost_samples 
*lost,
+                                       struct perf_record_lost_samples 
**plost,
                                        int cpu_idx, int thread_idx, 
u64 lost_count,
                                        u16 misc_flag)
 {
        struct perf_sample_id *sid;
        struct perf_sample sample = {};
+       struct perf_record_lost_samples *lost = *plost;
        int id_hdr_size;

+       if (!lost) {
+               lost = zalloc(PERF_SAMPLE_MAX_SIZE);
+               if (!lost) {
+                       pr_debug("Memory allocation failed\n");
+                       return;
+               }
+               lost->header.type = PERF_RECORD_LOST_SAMPLES;
+               *plost = lost;
+       }
+
        lost->lost = lost_count;
        if (evsel->core.ids) {
                sid = xyarray__entry(evsel->core.sample_id, cpu_idx, 
thread_idx);
@@ -1912,21 +1923,13 @@ static void __record__save_lost_samples(struct 
record *rec, struct evsel *evsel,
 static void record__read_lost_samples(struct record *rec)
 {
        struct perf_session *session = rec->session;
-       struct perf_record_lost_samples *lost;
+       struct perf_record_lost_samples *lost = NULL;
        struct evsel *evsel;

        /* there was an error during record__open */
        if (session->evlist == NULL)
                return;

-       lost = zalloc(PERF_SAMPLE_MAX_SIZE);
-       if (lost == NULL) {
-               pr_debug("Memory allocation failed\n");
-               return;
-       }
-
-       lost->header.type = PERF_RECORD_LOST_SAMPLES;
-
        evlist__for_each_entry(session->evlist, evsel) {
                struct xyarray *xy = evsel->core.sample_id;
                u64 lost_count;
@@ -1949,7 +1952,7 @@ static void record__read_lost_samples(struct 
record *rec)
                                }

                                if (count.lost) {
-                                       __record__save_lost_samples(rec, 
evsel, lost,
+                                       __record__save_lost_samples(rec, 
evsel, &lost,
                                                                    x, 
y, count.lost, 0);
                                }
                        }
@@ -1957,11 +1960,12 @@ static void record__read_lost_samples(struct 
record *rec)

                lost_count = perf_bpf_filter__lost_count(evsel);
                if (lost_count)
-                       __record__save_lost_samples(rec, evsel, lost, 0, 
0, lost_count,
+                       __record__save_lost_samples(rec, evsel, &lost, 
0, 0, lost_count,

PERF_RECORD_MISC_LOST_SAMPLES_BPF);
        }
 out:
-       free(lost);
+       if (lost)
+               free(lost);
 }

 static volatile sig_atomic_t workload_exec_errno;


Thanks,
Yang