On 05/07/13 16:24, Namhyung Kim wrote: > Hi Adrian, > > On Thu, Jul 4, 2013 at 10:20 PM, Adrian Hunter <[email protected]> > wrote: >> The event stream is not always parsable because the format of a sample >> is dependent on the sample_type of the selected event. When there >> is more than one selected event and the sample_types are not the >> same then parsing becomes problematic. A sample can be matched to its >> selected event using the ID that is allocated when the event is opened. >> Unfortunately, to get the ID from the sample means first parsing it. >> >> This patch adds a new sample format bit PERF_SAMPLE_IDENTIFER that puts >> the ID at a fixed position so that the ID can be retrieved without >> parsing the sample. For sample events, that is the first position >> immediately after the header. For non-sample events, that is the last >> position. > > Why do we have to keep another ID again?
It is a different place for the ID not another ID. > If all we need is the sample_type, why not just saving it directly? We really want to associate the event with the attribute so the ID is needed, not just the sample type. > > And for the implementation, I guess it'll break old perf tools > by parsing invalid position of data. IOW if it's recorded on a newer > kernel/tool and then reported on an older perf tool (maybe on a > different machine). In this case the old tool cannot recognize the > PERF_SAMPLE_IDENTIFIER and try to parse it as a different > type of data, right? I have changed the code so that PERF_SAMPLE_IDENTIFIER is only used for non-matching sample types. Since in those cases the data was anyway not parsable, the scenario you outline cannot happen. > > So I suggest put the data at the end of sample data like other new > sample types added. Older tools would simply ignore that part, and > newer tools can access it directly by checking event.header.size > and/or evsel->sample_size. The ID will be on the end of non-sample (e.g. mmap, comm, task) events, so if tools are parsing those events backwards (as perf tools does) then they will anyway fail if they are not expecting PERF_SAMPLE_IDENTIFIER. However that scenario only happens when the data is anyway not parsable as I mentioned above. > > Thanks, > Namhyung > >> >> Signed-off-by: Adrian Hunter <[email protected]> >> --- >> include/uapi/linux/perf_event.h | 3 ++- >> kernel/events/core.c | 11 ++++++++++- >> 2 files changed, 12 insertions(+), 2 deletions(-) >> >> diff --git a/include/uapi/linux/perf_event.h >> b/include/uapi/linux/perf_event.h >> index 0b1df41..6bb217e 100644 >> --- a/include/uapi/linux/perf_event.h >> +++ b/include/uapi/linux/perf_event.h >> @@ -134,8 +134,9 @@ enum perf_event_sample_format { >> PERF_SAMPLE_STACK_USER = 1U << 13, >> PERF_SAMPLE_WEIGHT = 1U << 14, >> PERF_SAMPLE_DATA_SRC = 1U << 15, >> + PERF_SAMPLE_IDENTIFIER = 1U << 16, >> >> - PERF_SAMPLE_MAX = 1U << 16, /* non-ABI */ >> + PERF_SAMPLE_MAX = 1U << 17, /* non-ABI */ >> }; >> >> /* >> diff --git a/kernel/events/core.c b/kernel/events/core.c >> index 1db3af9..ca532f2 100644 >> --- a/kernel/events/core.c >> +++ b/kernel/events/core.c >> @@ -1203,6 +1203,9 @@ static void perf_event__id_header_size(struct >> perf_event *event) >> if (sample_type & PERF_SAMPLE_TIME) >> size += sizeof(data->time); >> >> + if (sample_type & PERF_SAMPLE_IDENTIFIER) >> + size += sizeof(data->id); >> + >> if (sample_type & PERF_SAMPLE_ID) >> size += sizeof(data->id); >> >> @@ -4229,7 +4232,7 @@ static void __perf_event_header__init_id(struct >> perf_event_header *header, >> if (sample_type & PERF_SAMPLE_TIME) >> data->time = perf_clock(); >> >> - if (sample_type & PERF_SAMPLE_ID) >> + if (sample_type & (PERF_SAMPLE_ID | PERF_SAMPLE_IDENTIFIER)) >> data->id = primary_event_id(event); >> >> if (sample_type & PERF_SAMPLE_STREAM_ID) >> @@ -4268,6 +4271,9 @@ static void __perf_event__output_id_sample(struct >> perf_output_handle *handle, >> >> if (sample_type & PERF_SAMPLE_CPU) >> perf_output_put(handle, data->cpu_entry); >> + >> + if (sample_type & PERF_SAMPLE_IDENTIFIER) >> + perf_output_put(handle, data->id); >> } >> >> void perf_event__output_id_sample(struct perf_event *event, >> @@ -4380,6 +4386,9 @@ void perf_output_sample(struct perf_output_handle >> *handle, >> >> perf_output_put(handle, *header); >> >> + if (sample_type & PERF_SAMPLE_IDENTIFIER) >> + perf_output_put(handle, data->id); >> + >> if (sample_type & PERF_SAMPLE_IP) >> perf_output_put(handle, data->ip); >> >> -- >> 1.7.11.7 >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
