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SubjectRe: [PATCH] perf synthetic-events: save 4kb from 2 stack frames
On Thu, Mar 26, 2020 at 11:36:51PM -0700, Ian Rogers wrote:
> Reduce the scope of PATH_MAX sized char buffers so that the compiler can
> overlap their usage.
>
> perf_event__synthesize_mmap_events before 'sub $0x45b8,%rsp' after
> 'sub $0x35b8,%rsp'.
>
> perf_event__get_comm_ids before 'sub $0x2028,%rsp' after 'sub $0x1028,%rsp'.

nice catch.. is this actualy problem somewhere? I thought
we don't need to care that much about this in user space

jirka

>
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
> tools/perf/util/synthetic-events.c | 46 ++++++++++++++++++------------
> 1 file changed, 27 insertions(+), 19 deletions(-)
>
> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index 3f28af39f9c6..9ff54707bb30 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
> @@ -70,7 +70,6 @@ int perf_tool__process_synth_event(struct perf_tool *tool,
> static int perf_event__get_comm_ids(pid_t pid, char *comm, size_t len,
> pid_t *tgid, pid_t *ppid)
> {
> - char filename[PATH_MAX];
> char bf[4096];
> int fd;
> size_t size = 0;
> @@ -80,12 +79,16 @@ static int perf_event__get_comm_ids(pid_t pid, char *comm, size_t len,
> *tgid = -1;
> *ppid = -1;
>
> - snprintf(filename, sizeof(filename), "/proc/%d/status", pid);
> + {
> + char filename[PATH_MAX];
>
> - fd = open(filename, O_RDONLY);
> - if (fd < 0) {
> - pr_debug("couldn't open %s\n", filename);
> - return -1;
> + snprintf(filename, sizeof(filename), "/proc/%d/status", pid);
> +
> + fd = open(filename, O_RDONLY);
> + if (fd < 0) {
> + pr_debug("couldn't open %s\n", filename);
> + return -1;
> + }
> }
>
> n = read(fd, bf, sizeof(bf) - 1);
> @@ -280,7 +283,6 @@ int perf_event__synthesize_mmap_events(struct perf_tool *tool,
> struct machine *machine,
> bool mmap_data)
> {
> - char filename[PATH_MAX];
> FILE *fp;
> unsigned long long t;
> bool truncation = false;
> @@ -292,18 +294,22 @@ int perf_event__synthesize_mmap_events(struct perf_tool *tool,
> if (machine__is_default_guest(machine))
> return 0;
>
> - snprintf(filename, sizeof(filename), "%s/proc/%d/task/%d/maps",
> - machine->root_dir, pid, pid);
> +#define FILENAME_FMT_STRING "%s/proc/%d/task/%d/maps"
> + {
> + char filename[PATH_MAX];
>
> - fp = fopen(filename, "r");
> - if (fp == NULL) {
> - /*
> - * We raced with a task exiting - just return:
> - */
> - pr_debug("couldn't open %s\n", filename);
> - return -1;
> - }
> + snprintf(filename, sizeof(filename), FILENAME_FMT_STRING,
> + machine->root_dir, pid, pid);
>
> + fp = fopen(filename, "r");
> + if (fp == NULL) {
> + /*
> + * We raced with a task exiting - just return:
> + */
> + pr_debug("couldn't open %s\n", filename);
> + return -1;
> + }
> + }
> event->header.type = PERF_RECORD_MMAP2;
> t = rdclock();
>
> @@ -320,10 +326,10 @@ int perf_event__synthesize_mmap_events(struct perf_tool *tool,
> break;
>
> if ((rdclock() - t) > timeout) {
> - pr_warning("Reading %s time out. "
> + pr_warning("Reading " FILENAME_FMT_STRING " time out. "
> "You may want to increase "
> "the time limit by --proc-map-timeout\n",
> - filename);
> + machine->root_dir, pid, pid);
> truncation = true;
> goto out;
> }
> @@ -412,6 +418,8 @@ int perf_event__synthesize_mmap_events(struct perf_tool *tool,
>
> fclose(fp);
> return rc;
> +
> +#undef FILENAME_FMT_STRING
> }
>
> int perf_event__synthesize_modules(struct perf_tool *tool, perf_event__handler_t process,
> --
> 2.25.1.696.g5e7596f4ac-goog
>

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