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Are users expected to use cache allocation >>> while PLZA is enabled? Since only one resource group can be assigned I expect >>> there to be quite a few sharp corners when both are in use. Kernel work done >>> on behalf of high as well as low priority work will use the same cache allocations >>> and thus neither could actually get full benefit from having dedicated cache >>> portions? >> >> The best-known use case today is to leave both cache allocation and >> memory bandwidth allocation at their default (maximum) settings and >> enable PLZA on all CPUs. > > Interesting. This sounds like all kernel work can access the entire cache > and thus evict data from any user space tasks that may have used cache allocation > to avoid interference. > >> >> Users can, however, configure both cache allocation and memory bandwidth limits. In those cases, there can be corner-case behaviors and trade-offs. >> >> If you think the current wording is misleading, I can drop that text and rephrase it along these lines to include both cache and memory. > > No, the wording is not misleading. The description just focuses on memory bandwidth > allocation leaving impression that the feature only applies to that resource when it > applies to all resources. > >> >> "When cache and/or memory bandwidth associated with a CLOSID is >> aggressively throttled, and a task with that CLOSID moves into >> kernel mode, the kernel operations are also aggressively throttled. >> This can stall forward progress and eventually degrade overall >> system performance. >> >> AMD hardware supports the Privilege Level Zero Association (PLZA) >> feature, which allows the CPU's CLOSID and/or RMID association to be >> changed during transitions from user mode to kernel mode. This >> enables the kernel to run with a different CLOSID and/or RMID than >> user space, improving system performance and/or allowing kernel work >> to be monitored separately."> > > I think what you have for memory bandwidth sounds good. I do not think > the cache allocation and memory bandwidth usage descriptions should be > mixed since the implications are so different. Could you please just > add a snippet that highlights since the feature assigns CLOSID/RMID to > kernel work it influences allocation and monitoring of all resources, > not just memory bandwidth? > Yes. Sure. Thanks Babu