Re: [Xen-devel] [PATCH 4/4] tools/xenalyze: Allow automatic resizing of sample buffers

[anshul makkar <anshul.makkar@xxxxxxxxxx>]

On 08/08/16 10:54, George Dunlap wrote:
> Rather than have large fixed-size buffers, start with smaller buffers
> and allow them to grow as needed (doubling each time), with a fairly
> large maximum.  Allow this maximum to be set by a command-line
> parameter.
>
> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
> ---
> CC: Ian Jackson <ian.jackson@xxxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
> CC: Anshul Makkar <anshul.makkar@xxxxxxxxxx>
> ---
>   tools/xentrace/xenalyze.c | 95 +++++++++++++++++++++++++++++++++--------------
>   1 file changed, 68 insertions(+), 27 deletions(-)
>
> diff --git a/tools/xentrace/xenalyze.c b/tools/xentrace/xenalyze.c
> index 455cbdf..a4d8823 100644
> --- a/tools/xentrace/xenalyze.c
> +++ b/tools/xentrace/xenalyze.c
> @@ -44,7 +44,8 @@ struct mread_ctrl;
>   #define QHZ_FROM_HZ(_hz) (((_hz) << 10)/ 1000000000)
>
>   #define ADDR_SPACE_BITS 48
> -#define DEFAULT_SAMPLE_SIZE 10240
> +#define DEFAULT_SAMPLE_SIZE 1024
> +#define DEFAULT_SAMPLE_MAX  1024*1024*32
>   #define DEFAULT_INTERVAL_LENGTH 1000
>       s->event_count++;
>
>       if (!c)
>           return;
>
>       if(opt.sample_size) {
> -        int lap = (s->count/opt.sample_size)+1,
> -            index =s->count % opt.sample_size;
> -        if((index - (lap/3))%lap == 0) {
> -            if(!s->sample) {
> -                s->sample = malloc(sizeof(*s->sample) * opt.sample_size);
> -                if(!s->sample) {
> -                    fprintf(stderr, "%s: malloc failed!\n", __func__);
> -                    error(ERR_SYSTEM, NULL);
> -                }
> +        if (s->count >= s->sample_size
> +            && (s->count == 0
> +                || opt.sample_max == 0
> +                || s->sample_size < opt.sample_max)) {
> +            int new_size;
> +            void * new_sample = NULL;
> +
> +            new_size = s->sample_size << 1;
Sorry for my ignorance here, but why we have chosen to double the size. 
Can't we increase by fixed size X where X < double size. Are we sure 
that we will be able to fully utilize the double sized buffer.
> +
> +            if (new_size == 0)
> +                new_size = opt.sample_size;
> +
> +            if (opt.sample_max != 0 && new_size > opt.sample_max)
> +                new_size = opt.sample_max;
> +
> +            //printf("New size: %d\n", new_size);
> +
> +            new_sample = realloc(s->sample, sizeof(*s->sample) * new_size);
> +
> +            if (new_sample) {
> +                s->sample = new_sample;
> +                s->sample_size = new_size;
>               }
> -            s->sample[index]=c;
>           }
> +
> +        if (s->count < s->sample_size) {
> +            s->sample[s->count]=c;
> +        } else {
> +            /*
> +             * If we run out of space for samples, start taking only a
> +             * subset of samples.
> +             */
> +            int lap, index;
> +            lap = (s->count/s->sample_size)+1;
> +            index =s->count % s->sample_size;
> +            if((index - (lap/3))%lap == 0) {
> +                s->sample[index]=c;
> +             }
> +         }
>       }
>       s->count++;
>

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