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    SubjectRe: [PATCH v2 6/6] perf cpumap: Add range data encoding
    On Tue, Jun 14, 2022 at 07:33:53AM -0700, Ian Rogers wrote:

    SNIP

    > -static size_t cpus_size(const struct perf_cpu_map *map)
    > +static void synthesize_range_cpus(struct synthesize_cpu_map_data *data)
    > {
    > - return sizeof(struct cpu_map_entries) + perf_cpu_map__nr(map) * sizeof(u16);
    > + data->data->type = PERF_CPU_MAP__RANGE_CPUS;
    > + data->data->range_cpu_data.any_cpu = data->has_any_cpu;
    > + data->data->range_cpu_data.start_cpu = data->min_cpu;
    > + data->data->range_cpu_data.end_cpu = data->max_cpu;
    > }
    >
    > -static size_t mask_size(const struct perf_cpu_map *map, int *max)
    > -{
    > - *max = perf_cpu_map__max(map).cpu;
    > - return sizeof(struct perf_record_mask_cpu_map32) + BITS_TO_U32(*max) * sizeof(__u32);
    > -}
    > -
    > -static void *cpu_map_data__alloc(const struct perf_cpu_map *map, size_t *size,
    > - u16 *type, int *max)
    > +static void *cpu_map_data__alloc(struct synthesize_cpu_map_data *syn_data,
    > + size_t header_size)
    > {
    > size_t size_cpus, size_mask;
    > - bool is_dummy = perf_cpu_map__empty(map);
    >
    > - /*
    > - * Both array and mask data have variable size based
    > - * on the number of cpus and their actual values.
    > - * The size of the 'struct perf_record_cpu_map_data' is:
    > - *
    > - * array = size of 'struct cpu_map_entries' +
    > - * number of cpus * sizeof(u64)
    > - *
    > - * mask = size of 'struct perf_record_record_cpu_map' +
    > - * maximum cpu bit converted to size of longs
    > - *
    > - * and finally + the size of 'struct perf_record_cpu_map_data'.
    > - */
    > - size_cpus = cpus_size(map);
    > - size_mask = mask_size(map, max);
    > + syn_data->nr = perf_cpu_map__nr(syn_data->map);
    > + syn_data->has_any_cpu = (perf_cpu_map__cpu(syn_data->map, 0).cpu == -1) ? 1 : 0;

    I'm bit lost in the logic in here.. should it be '.cpu != -1' ?
    has_any_cpu is named as bool but used as index below ;-)

    could you please keep/update the comment above and explain
    the conditions when each cpu_map type is taken

    thanks,
    jirka

    >
    > - if (is_dummy || (size_cpus < size_mask)) {
    > - *size += size_cpus;
    > - *type = PERF_CPU_MAP__CPUS;
    > - } else {
    > - *size += size_mask;
    > - *type = PERF_CPU_MAP__MASK;
    > + syn_data->min_cpu = perf_cpu_map__cpu(syn_data->map, syn_data->has_any_cpu).cpu;
    > + syn_data->max_cpu = perf_cpu_map__max(syn_data->map).cpu;
    > + if (syn_data->max_cpu - syn_data->min_cpu + 1 == syn_data->nr - syn_data->has_any_cpu) {
    > + /* A consecutive range of CPUs can be encoded using a range. */
    > + assert(sizeof(u16) + sizeof(struct perf_record_range_cpu_map) == sizeof(u64));
    > + syn_data->type = PERF_CPU_MAP__RANGE_CPUS;
    > + syn_data->size = header_size + sizeof(u64);
    > + return zalloc(syn_data->size);
    > }
    >
    > - *size += sizeof(__u16); /* For perf_record_cpu_map_data.type. */
    > - *size = PERF_ALIGN(*size, sizeof(u64));
    > - return zalloc(*size);
    > + size_cpus = sizeof(u16) + sizeof(struct cpu_map_entries) + syn_data->nr * sizeof(u16);
    > + /* Due to padding, the 4bytes per entry mask variant is always smaller. */
    > + size_mask = sizeof(u16) + sizeof(struct perf_record_mask_cpu_map32) +
    > + BITS_TO_U32(syn_data->max_cpu) * sizeof(__u32);
    > + if (syn_data->has_any_cpu || size_cpus < size_mask) {
    > + /* Follow the CPU map encoding. */
    > + syn_data->type = PERF_CPU_MAP__CPUS;
    > + syn_data->size = header_size + PERF_ALIGN(size_cpus, sizeof(u64));
    > + return zalloc(syn_data->size);
    > + }
    > + /* Encode using a bitmask. */
    > + syn_data->type = PERF_CPU_MAP__MASK;
    > + syn_data->size = header_size + PERF_ALIGN(size_mask, sizeof(u64));
    > + return zalloc(syn_data->size);

    SNIP

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