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

[Frederic Weisbecker <fweisbec@gmail.com>]

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;
>  		}
>  	}
> 
>