On 01/02/15 20:06, Jiri Olsa wrote:
> On Thu, Jan 29, 2015 at 05:06:55PM +0900, Namhyung Kim wrote:
>> The new --index option will create indexed data file which can be
>> processed by multiple threads parallelly. It saves meta event and
>> sample data in separate files and merges them with an index table.
>>
>> To build an index table, it needs to know exact offsets and sizes for
>> each sample data. However the offset only can be calculated after the
>> feature data is fixed, and to save feature data it needs to access to
>> the sample data because it needs to mark used DSOs for build-id table.
>>
>> So I ended up with reserving 1MB hole for the feature data area and then
>> put sample data and calculated offsets. Now an indexed perf data file
>> will look like below:
>>
>> +---------------------+
>> | file header |
>> |---------------------|
>> | |
>> | meta events |
>> | |
>> |---------------------|
>> | feature data |
>> | (contains index) -+--+
>> |---------------------| |
>> | ~1MB hole | |
>> |---------------------| |
>> | | |
>> | sample data[1] <-+--+
>> | | |
>> |---------------------| |
>> | | |
>> | sample data[2] <-|--+
>> | | |
>> |---------------------| |
>> | ... | ...
>> +---------------------+
>
> I also dont see how to store it in a nice way under current header layout,
> but how about bump up the header version for this feature? ;-)
>
> currently it's:
>
> struct perf_file_header {
> u64 magic;
> u64 size;
> u64 attr_size;
> struct perf_file_section attrs;
> struct perf_file_section data;
> /* event_types is ignored */
> struct perf_file_section event_types;
> DECLARE_BITMAP(adds_features, HEADER_FEAT_BITS);
> };
>
>
> - we already store attrs as a FEATURE so we could omit that
> - your patch stores only synthesized data into 'data' section (-1 idx)
> this could be stored into separate file and get merged with the rest
> - new header version would have 'features' section, so the features
> position wouldnt depend on the 'data' end as of now and we could
> easily store after all data is merged:
>
> struct perf_file_header {
> u64 magic;
> u64 size;
> u64 attr_size;
> struct perf_file_section features;
> DECLARE_BITMAP(adds_features, HEADER_FEAT_BITS);
> };
>
>
> thoughts?
How come the features are being written before the sample data anyway?
I would have expected:
- write the data (update the index in memory)
- write the features (including index)
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