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

Alexey Budankov
2019-03-07T14:51:53Z

On 07.03.2019 14:59, Jiri Olsa wrote:
> On Thu, Mar 07, 2019 at 11:26:16AM +0300, Alexey Budankov wrote:
>>
>> 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 (+=).
>
> and then process_header(, 0) is called again no?

Yes, in the next iteration these three steps repeat for the next record.

~Alexey

>
> jirka
>