> On Aug 26, 2022, at 11:25 PM, Namhyung Kim <namhyung@xxxxxxxxxx> wrote: > > On Fri, Aug 26, 2022 at 2:26 PM Song Liu <songliubraving@xxxxxx> wrote: >> >> >> >>> On Aug 26, 2022, at 2:12 PM, Namhyung Kim <namhyung@xxxxxxxxxx> wrote: >>> >>> On Fri, Aug 26, 2022 at 1:59 PM Song Liu <songliubraving@xxxxxx> wrote: >>>> >>>> >>>> >>>>> On Aug 26, 2022, at 12:30 PM, Namhyung Kim <namhyung@xxxxxxxxxx> wrote: >>>>> >>>>> On Fri, Aug 26, 2022 at 11:45 AM Song Liu <songliubraving@xxxxxx> wrote: >>>>> >>>>>>> And actually, we can just read ctx->data and get the raw record, >>>>>>> right..? >>>>>> >>>>>> Played with this for a little bit. ctx->data appears to be not >>>>>> reliable sometimes. I guess (not 100% sure) this is because we >>>>>> call bpf program before event->orig_overflow_handler. We can >>>>>> probably add a flag to specify we want to call orig_overflow_handler >>>>>> first. >>>>> >>>>> I'm not sure. The sample_data should be provided by the caller >>>>> of perf_event_overflow. So I guess the bpf program should see >>>>> a valid ctx->data. >>>> >>>> Let's dig into this. Maybe we need some small changes in >>>> pe_prog_convert_ctx_access. >>> >>> Sure, can you explain the problem in detail and share your program? >> >> I push the code to >> >> https://git.kernel.org/pub/scm/linux/kernel/git/song/linux.git/log/?h=test-perf-event >> >> The code is in tools/bpf/perf-test/. >> >> The problem is we cannot get reliable print of data->cpu_entry in >> /sys/kernel/tracing/trace. > > Ah, right. I've realized that the sample data is passed before full > initialized. Please see perf_sample_data_init(). The other members > are initialized right before written to the ring buffer in the > orig_overflow_handler (__perf_event_output). > > That explains why pe_prog_convert_ctx_access() handles > data and period specially. We need to handle it first. Thanks for confirming this. I guess we will need a helper (or kfunc) for the raw data. Shall we make it more generic that we can get other PERF_SAMPLE_*? Thanks, Song
