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Subject: Re: [PATCH v3 20/50] perf record: Be lazier in allocating lost
 samples buffer
To:     Ian Rogers <irogers@google.com>
References: <20231024222353.3024098-1-irogers@google.com>
 <20231024222353.3024098-21-irogers@google.com>
From:   Yang Jihong <yangjihong1@huawei.com>
CC:     Ian Rogers <irogers@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Nick Terrell <terrelln@fb.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Andi Kleen <ak@linux.intel.com>, Leo Yan <leo.yan@linaro.org>,
        Song Liu <song@kernel.org>,
        Sandipan Das <sandipan.das@amd.com>,
        James Clark <james.clark@arm.com>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Miguel Ojeda <ojeda@kernel.org>,
        Liam Howlett <liam.howlett@oracle.com>,
        Athira Rajeev <atrajeev@linux.vnet.ibm.com>,
        Kajol Jain <kjain@linux.ibm.com>,
        K Prateek Nayak <kprateek.nayak@amd.com>,
        Sean Christopherson <seanjc@google.com>,
        Yanteng Si <siyanteng@loongson.cn>,
        Ravi Bangoria <ravi.bangoria@amd.com>,
        German Gomez <german.gomez@arm.com>,
        Changbin Du <changbin.du@huawei.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        liuwenyu <liuwenyu7@huawei.com>, <linux-kernel@vger.kernel.org>,
        <linux-perf-users@vger.kernel.org>
Message-ID: <7516348d-fe6d-9768-049e-328cfcda89ee@huawei.com>
Date:   Wed, 25 Oct 2023 11:44:19 +0800
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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@google.com>
> ---
>   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