Hi Ilpo, 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. > >>>>> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx> >>>>> --- >>>>> tools/testing/selftests/resctrl/cat_test.c | 68 +++++++++++++++++-- >>>>> tools/testing/selftests/resctrl/resctrl.h | 1 + >>>>> .../testing/selftests/resctrl/resctrl_tests.c | 1 + >>>>> 3 files changed, 63 insertions(+), 7 deletions(-) >>>>> >>>>> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c >>>>> index 48a96acd9e31..a9c72022bb5a 100644 >>>>> --- a/tools/testing/selftests/resctrl/cat_test.c >>>>> +++ b/tools/testing/selftests/resctrl/cat_test.c >>>>> @@ -131,8 +131,47 @@ void cat_test_cleanup(void) >>>>> remove(RESULT_FILE_NAME); >>>>> } >>>>> >>>>> +/* >>>>> + * L2 CAT test measures L2 misses indirectly using L3 accesses as a proxy >>>>> + * because perf cannot directly provide the number of L2 misses (there are >>>>> + * only platform specific ways to get the number of L2 misses). >>>>> + * >>>>> + * This function sets up L3 CAT to reduce noise from other processes during >>>>> + * L2 CAT test. >>>> >>>> This motivation is not clear to me. Does the same isolation used during >>>> L3 CAT testing not work? I expected it to follow the same idea with the >>>> L2 cache split in two, the test using one part and the rest of the >>>> system using the other. Is that not enough isolation? >>> >>> Isolation for L2 is done very same way as with L3 and I think it itself >>> works just fine. >>> >>> However, because L2 CAT selftest as is measures L3 accesses that in ideal >>> world equals to L2 misses, isolating selftest related L3 accesses from the >>> rest of the system should reduce noise in the # of L3 accesses. It's not >>> mandatory though so if L3 CAT is not available the function just prints a >>> warning about the potential noise and does setup nothing for L3. >> >> This is not clear to me. If the read misses L2 and then accesses L3 then >> it should not matter which part of L3 cache the work is isolated to. >> What noise do you have in mind? > > The way it is currently done is to measure L3 accesses. If something else > runs at the same time as the CAT selftest, it can do mem accesses that > cause L3 accesses which is noise in the # of L3 accesses number since > those accesses were unrelated to the L2 CAT selftest. > Creating a CAT allocation sets aside a portion of cache where a task/cpu can allocation into cache, it does not prevent one task from accessing the cache concurrently with another. Reinette
