Re: [PATCH 05/10] perf-record: Share per-cpu buffers

Frederic Weisbecker
2010-05-21T09:44:30Z

On Fri, May 21, 2010 at 11:02:06AM +0200, Peter Zijlstra wrote:
> It seems a waste of space to create a buffer per event, share it per-cpu.
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
> tools/perf/builtin-record.c | 52 +++++++++++++++++++++++---------------------
> 1 file changed, 28 insertions(+), 24 deletions(-)
>
> Index: linux-2.6/tools/perf/builtin-record.c
> ===================================================================
> --- linux-2.6.orig/tools/perf/builtin-record.c
> +++ linux-2.6/tools/perf/builtin-record.c
> @@ -85,7 +85,7 @@ struct mmap_data {
> unsigned int prev;
> };
>
> -static struct mmap_data *mmap_array[MAX_NR_CPUS][MAX_COUNTERS];
> +static struct mmap_data mmap_array[MAX_NR_CPUS];
>
> static unsigned long mmap_read_head(struct mmap_data *md)
> {
> @@ -380,18 +380,29 @@ try_again:
> if (group && group_fd == -1)
> group_fd = fd[nr_cpu][counter][thread_index];
>
> - event_array[nr_poll].fd = fd[nr_cpu][counter][thread_index];
> - event_array[nr_poll].events = POLLIN;
> - nr_poll++;
> -
> - mmap_array[nr_cpu][counter][thread_index].counter = counter;
> - mmap_array[nr_cpu][counter][thread_index].prev = 0;
> - mmap_array[nr_cpu][counter][thread_index].mask = mmap_pages*page_size - 1;
> - mmap_array[nr_cpu][counter][thread_index].base = mmap(NULL, (mmap_pages+1)*page_size,
> - PROT_READ|PROT_WRITE, MAP_SHARED, fd[nr_cpu][counter][thread_index], 0);
> - if (mmap_array[nr_cpu][counter][thread_index].base == MAP_FAILED) {
> - error("failed to mmap with %d (%s)\n", errno, strerror(errno));
> - exit(-1);
> + if (counter || thread_index) {
> + ret = ioctl(fd[nr_cpu][counter][thread_index],
> + PERF_EVENT_IOC_SET_OUTPUT,
> + fd[nr_cpu][0][0]);
> + if (ret) {
> + error("failed to set output: %d (%s)\n", errno,
> + strerror(errno));
> + exit(-1);
> + }
> + } else {
> + mmap_array[nr_cpu].counter = counter;
> + mmap_array[nr_cpu].prev = 0;
> + mmap_array[nr_cpu].mask = mmap_pages*page_size - 1;

If you do this multiplex per cpu (which I think is a very good thing), you
should also increase the default value of mmap_pages as it might not be big
enough anymore.

> + mmap_array[nr_cpu].base = mmap(NULL, (mmap_pages+1)*page_size,
> + PROT_READ|PROT_WRITE, MAP_SHARED, fd[nr_cpu][counter][thread_index], 0);
> + if (mmap_array[nr_cpu].base == MAP_FAILED) {
> + error("failed to mmap with %d (%s)\n", errno, strerror(errno));
> + exit(-1);
> + }
> +
> + event_array[nr_poll].fd = fd[nr_cpu][counter][thread_index];
> + event_array[nr_poll].events = POLLIN;
> + nr_poll++;
> }
>
> if (filter != NULL) {
> @@ -492,16 +503,11 @@ static struct perf_event_header finished
>
> static void mmap_read_all(void)
> {
> - int i, counter, thread;
> + int i;
>
> for (i = 0; i < nr_cpu; i++) {
> - for (counter = 0; counter < nr_counters; counter++) {
> - for (thread = 0; thread < thread_num; thread++) {
> - if (mmap_array[i][counter][thread].base)
> - mmap_read(&mmap_array[i][counter][thread]);
> - }
> -
> - }
> + if (mmap_array[i].base)
> + mmap_read(&mmap_array[i]);
> }
>
> if (perf_header__has_feat(&session->header, HEADER_TRACE_INFO))
> @@ -876,9 +882,7 @@ int cmd_record(int argc, const char **ar
> for (i = 0; i < MAX_NR_CPUS; i++) {
> for (j = 0; j < MAX_COUNTERS; j++) {
> fd[i][j] = malloc(sizeof(int)*thread_num);
> - mmap_array[i][j] = zalloc(
> - sizeof(struct mmap_data)*thread_num);
> - if (!fd[i][j] || !mmap_array[i][j])
> + if (!fd[i][j])
> return -ENOMEM;
> }
> }
>
>