Messages in this thread | | | Subject | Re: [PATCH v2 2/2] perf mem: Support HITM for when mem_lvl_num is used | From | German Gomez <> | Date | Mon, 14 Mar 2022 18:00:13 +0000 |
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Hi Leo, Ali
On 14/03/2022 06:33, Leo Yan wrote: > On Sun, Mar 13, 2022 at 07:19:33PM +0000, Ali Saidi wrote: > > [...] > >>>>> + if (lvl & P(LVL, L3) || lnum == P(LVLNUM, L4)) { >>>> According to a comment in the previous patch, using L4 is specific to Neoverse, right? >>>> >>>> Maybe we need to distinguish the Neoverse case from the generic one here as well >>>> >>>> if (is_neoverse) >>>> // treat L4 as llc >>>> else >>>> // treat L3 as llc >>> I personally think it's not good idea to distinguish platforms in the decoding code. >> I agree here. The more we talk about this, the more I'm wondering if we're >> spending too much code solving a problem that doesn't exist. I know of no >> Neoverse systems that actually have 4 cache levels, they all actually have three >> even though it's technically possible to have four. I have some doubts anyone >> will actually build four levels of cache and perhaps the most prudent path here >> is to assume only three levels (and adjust the previous patch) until someone >> actually produces a system with four levels instead of a lot of code that is >> never actually exercised? > I am not right person to say L4 cache is not implemented in Neoverse > platforms; my guess for a "System cache" data source might be L3 or > L4 and it is a implementation dependent. Maybe German or Arm mates > could confirm for this.
I had a look at the TRMs for the N1[1], V1[2] and N2[3] Neoverse cores (specifically the LL_CACHE_RD pmu events). If we were to assign a number to the system cache (assuming all caches are implemented):
*For N1*, if L2 and L3 are implemented, system cache would follow at *L4*
*For V1 and N2*, if L2 is implemented, system cache would follow at *L3* (these don't seem to have the same/similar per-cluster L3 cache from the N1)
There's also room in the PERF_MEM_LVLNUM_* namespace for a SYSTEM value, if we want to consider that option as well.
[1] https://developer.arm.com/documentation/100616/0401/?lang=en [2] https://developer.arm.com/documentation/101427/0101/?lang=en [3] https://developer.arm.com/documentation/102099/0001/?lang=en
> > Thanks, > Leo
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