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Message-ID: <4d275fcd-a102-662f-d9f7-3acd3586acf2@huawei.com>
Date: Wed, 25 Oct 2023 10:38:51 +0800
From: Yang Jihong <yangjihong1@...wei.com>
To: Ian Rogers <irogers@...gle.com>
CC: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
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<linux-perf-users@...r.kernel.org>
Subject: Re: [PATCH v3 13/50] libperf: Lazily allocate mmap event copy
Hello,
On 2023/10/25 6:23, Ian Rogers wrote:
> The event copy in the mmap is used to have storage to a read
> event. Not all users of mmaps read the events, such as perf record, so
> switch the allocation to being on first read rather than being
> embedded within the perf_mmap.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
> tools/lib/perf/include/internal/mmap.h | 2 +-
> tools/lib/perf/mmap.c | 9 +++++++++
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/perf/include/internal/mmap.h b/tools/lib/perf/include/internal/mmap.h
> index 5a062af8e9d8..b11aaf5ed645 100644
> --- a/tools/lib/perf/include/internal/mmap.h
> +++ b/tools/lib/perf/include/internal/mmap.h
> @@ -33,7 +33,7 @@ struct perf_mmap {
> bool overwrite;
> u64 flush;
> libperf_unmap_cb_t unmap_cb;
> - char event_copy[PERF_SAMPLE_MAX_SIZE] __aligned(8);
> + void *event_copy;
> struct perf_mmap *next;
> };
>
> diff --git a/tools/lib/perf/mmap.c b/tools/lib/perf/mmap.c
> index 2184814b37dd..91ae46aac378 100644
> --- a/tools/lib/perf/mmap.c
> +++ b/tools/lib/perf/mmap.c
> @@ -51,6 +51,8 @@ int perf_mmap__mmap(struct perf_mmap *map, struct perf_mmap_param *mp,
>
> void perf_mmap__munmap(struct perf_mmap *map)
> {
> + free(map->event_copy);
> + map->event_copy = NULL;
> if (map && map->base != NULL) {
> munmap(map->base, perf_mmap__mmap_len(map));
> map->base = NULL;
> @@ -226,6 +228,13 @@ static union perf_event *perf_mmap__read(struct perf_mmap *map,
> unsigned int len = min(sizeof(*event), size), cpy;
> void *dst = map->event_copy;
>
> + if (!dst) {
> + dst = malloc(PERF_SAMPLE_MAX_SIZE);
`event` is used as the return parameter of libperf API
perf_mmap__read_event().
Is `zalloc` better to avoid dirty data?
Thanks,
Yang
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