Re: [PATCH v5 07/10] perf record: implement -z,--compression_level=n option and compression

Alexey Budankov
2019-03-07T08:26:22Z

On 05.03.2019 15:26, Jiri Olsa wrote:
> On Fri, Mar 01, 2019 at 06:58:32PM +0300, Alexey Budankov wrote:
>
> SNIP
>
>> +static size_t record__process_comp_header(void *record, size_t increment)
>> +{
>> + struct compressed_event *event = record;
>> + size_t size = sizeof(struct compressed_event);
>> +
>> + if (increment) {
>> + event->header.size += increment;
>> + return increment;
>> + } else {
>> + event->header.type = PERF_RECORD_COMPRESSED;
>> + event->header.size = size;
>> + return size;
>> + }
>
> so zstd_compress_stream_to_records calls this in the loop:
>
> while (input.pos < input.size) {
> ...
> size = process_header(record, 0);
> ...
> size = process_header(record, size);
> }
>
> the header.size will get overwritten with every new iteration, no?

Every new record is headed by PERF_RECORD_COMPRESSED header an updated with
resulted compressed frame size after compression.

process_header(, 0) puts header, then
compression puts compressed frame, then
process_header(, N) updates header.size value (+=).

~Alexey

>
> jirka
>