On Mon, 6 Nov 2023, Reinette Chatre wrote:
On 11/6/2023 9:03 AM, Reinette Chatre wrote:
On 11/6/2023 1:53 AM, Ilpo Järvinen wrote:
On Fri, 3 Nov 2023, Reinette Chatre wrote:
On 11/3/2023 3:39 AM, Ilpo Järvinen wrote:
On Thu, 2 Nov 2023, Reinette Chatre wrote:
On 10/24/2023 2:26 AM, Ilpo Järvinen wrote:
> Add L2 CAT selftest. As measuring L2 misses is not easily available > with perf, use L3 accesses as a proxy for L2 CAT working or not.
I understand the exact measurement is not available but I do notice some L2 related symbolic counters when I run "perf list". l2_rqsts.all_demand_miss looks promising.
Okay, I was under impression that L2 misses are not available. Both based on what you mentioned to me half an year ago and because of what flags I found from the header. But I'll take another look into it.
You are correct that when I did L2 testing a long time ago I used the model specific L2 miss counts. I was hoping that things have improved so that model specific counters are not needed, as you have tried here. I found the l2_rqsts symbol while looking for alternatives but I am not familiar enough with perf to know how these symbolic names are mapped. I was hoping that they could be a simple drop-in replacement to experiment with.
According to perf_event_open() manpage, mapping those symbolic names requires libpfm so this would add a library dependency?
I do not see perf list using this library to determine the event and umask but I am in unfamiliar territory. I'll have to spend some more time here to determine options.
tools/perf/pmu-events/README cleared it up for me. The architecture specific tables are included in the perf binary. Potentially pmu-events.h could be included or the test could just stick with the architectural events. A quick look at the various cache.json files created the impression that the events of interest may actually have the same event code and umask across platforms. I am not familiar with libpfm. This can surely be considered if it supports this testing. Several selftests have library dependencies.
man perf_event_open() says this:
"If type is PERF_TYPE_RAW, then a custom "raw" config value is needed. Most CPUs support events that are not covered by the "generalized" events. These are implementation defined; see your CPU manual (for ex- ample the Intel Volume 3B documentation or the AMD BIOS and Kernel De- veloper Guide). The libpfm4 library can be used to translate from the name in the architectural manuals to the raw hex value perf_event_open() expects in this field."
...I've not come across libpfm myself either but to me it looks libpfm bridges between those architecture specific tables and perf_event_open(). That is, it could provide the binary value necessary in constructing the perf_event_attr struct.
I think this is probably the function which maps string -> perf_event_attr:
https://man7.org/linux/man-pages/man3/pfm_get_os_event_encoding.3.html