On 2021/4/22 11:49, Leo Yan wrote: > On Mon, Apr 19, 2021 at 09:03:18PM +0800, Yicong Yang wrote: >> On 2021/4/17 21:56, Alexander Shishkin wrote: >>> Yicong Yang <yangyicong@xxxxxxxxxxxxx> writes: >>> >>>> The reason for not using perf is because there is no current support >>>> for uncore tracing in the perf facilities. >>> >>> Not unless you count >>> >>> $ perf list|grep -ic uncore >>> 77 >>> >> >> these are uncore events probably do not support sampling. >> >> I tried on x86: >> >> # ./perf record -e uncore_imc_0/cas_count_read/ >> Error: >> The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (uncore_imc_0/cas_count_read/). >> /bin/dmesg | grep -i perf may provide additional information. >> >> For HiSilicon uncore PMUs, we don't support uncore sampling: >> >> 'The current driver does not support sampling. So "perf record" is unsupported. ' [1] >> >> and also in another PMU: >> >> 'PMU doesn't support process specific events and cannot be used in sampling mode.' [2] >> >> [1] Documentation/admin-guide/perf/hisi-pmu.rst >> [2] Documentation/admin-guide/perf/arm_dsu_pmu.rst > > I did some debugging for this, and yes, it's related with the event > doesn't support sampling for these x86 uncore events. > > So I can use below commands for the uncore event > 'uncore_imc/data_reads/' in my experiment: > > # perf record -e 'uncore_imc/data_reads/' --no-samples -- ls > # perf stat -e 'uncore_imc/data_reads/' -- ls > > For your case, I think you need to write the callback > pmu::event_init(), it should not forbid any tracing even if set > sampling, just like other perf event drive for support AUX tracing. > thanks for the hint! I didn't know much about perf so I only do the basic test. will further investigate on this. >>>> We have our own format >>>> of data and don't need perf doing the parsing. >>> >>> Perf has AUX buffers, which are used for all kinds of own formats. >>> >> >> ok. we thought perf will break the data format but AUX buffers seems won't. >> do we need to add full support for tracing as well as parsing or it's ok for >> not parsing it through perf? > > IMHO, this could divide into two parts. The first part is to enable > perf drive with support AUX tracing, and perf tool can capture the trace > data. The second part is to add the decoder in the perf tool so that > the developers can *consume* the trace data; for the decoder, you > could refer the codes: > > tools/perf/util/intel-pt-decoder/ > tools/perf/util/cs-etm-decoder/ > > Or Arm SPE case: > > tools/perf/util/arm-spe-decoder/ > will refer to these implementation to see how to add the decoder for our traced data. very detailed guidance! >>>> A similar approach for implementing this function is ETM, which use >>>> sysfs for configuring and a character device for dumping data. >>> >>> And also perf. One reason ETM has a sysfs interface is because the >>> driver predates perf's AUX buffers. Can't say if it's the only >>> reason. I'm assuming you're talking about Coresight ETM. > > I am not the best person to give background for this. Mathieu or Mike > could give more info for this. From my undersanding, Sysfs nodes can > be used as knobs for configuration, but it's difficult for profiling. > as explained by the maintainers that there are some historical reasons for having sysfs interfaces for ETM as there is no perf AUX buffers at beginning. I thought sysfs interface as an option but perf AUX buffer is better as suggested. > Let's think about for the profiling, if one developer uses the Sysfs > for the setting and read out the trace data, these informations are > discrete. If another developer wants to review the profiling result, > then all these info need to be shared together. > ok. make sense to me. > So we can benefit much from the perf tool for the usage, since all the > profiling context will be gathered (DSOs, hardware configuration which > can be saved into metadata), so the final profiling file can be easily > shared and more friendly for reviewing. > ok. it will be beneficial if we use perf for both tracing and decoding, as we'll also get addition information attached to the trace data. Considering we have two functions: tracing and tuning. For tracing we can make use of perf AUX buffer but for tuning, I still cannot see how to make use of perf. So probably we can make tuning go through sysfs? And Daniel suggested so. Appreciate for the suggestion and guidance! Regards, Yicong > Thanks, > Leo > > . >
