Hi André, On 14/05/2019 20:40, André Przywara wrote: > On 14/05/2019 18:20, James Morse wrote: >> On 10/05/2019 18:39, Andre Przywara wrote: >>> On Sat, 9 Feb 2019 18:50:39 -0800 >>> Fenghua Yu <[email protected]> wrote: >>>> From: Babu Moger <[email protected]> >>>> >>>> RESCTRL feature is supported both on Intel and AMD now. Some features >>>> are implemented differently. Add vendor detection mechanism. Use the vendor >>>> check where there are differences. >>> >>> I don't think vendor detection is the right approach. The Linux userland >>> interface should be even architecture agnostic, not to speak of different >>> vendors. >>> >>> But even if we need this for some reason ...
>> What do we need it for? Surely it indicates something is wrong with the >> kernel interface >> if you need to know which flavour of CPU this is. > > As you mentioned, we should not need it. I just couldn't find a better > way (yet) to differentiate between L3 cache ID and physical package ID > (see patch 11/13). So this is a kludge for now to not break this > particular code. [0]? That's broken. It needs to take the 'cache/index?/id' field, and not hard-code '3', search each 'cache/index?/level' instead. Documentation/x86/resctrl_ui.rst's "Cache IDs" section says: | On current generation systems there is one L3 cache per socket and L2 | caches are generally just shared by the hyperthreads on a core, but this | isn't an architectural requirement. [...] | So instead of using "socket" or "core" to define the set of logical cpus | sharing a resource we use a "Cache ID" [...] | To find the ID for each logical CPU look in | /sys/devices/system/cpu/cpu*/cache/index*/id arch/x86/kernel/cpu/restrl/core.c:domain_add_cpu() pulls the domain-id out of struct cacheinfo: | int id = get_cache_id(cpu, r->cache_level); drivers/base/cacheinfo.c has some macro-foliage that exports this same field via sysfs, and arch/x86/kernel/cpu/restrl/ctrlmondata.c:parse_line() matches that id against the value user-space provides in the schemata. (we've got some horrible code for arm64 to make this work without 'cache id' as a hardware property!) On x86 these numbers are of the order 0,1,2, so its very likely physical_package_id and cache_id alias, and you get away with it. > Out of curiosity: Is there any userland tool meant to control the > resources? I guess poking around in sysfs is not how admins are expected > to use this? I've come across: https://github.com/intel/intel-cmt-cat/ but I've never even cloned it. The rdtset man page has: | With --iface-os (-I) parameter, rdtset uses resctrl filesystem (/sys/fs/resctrl) | instead of accessing MSRs directly. > This tool would surely run into the same problems, which somewhat tell > me that the interface is not really right. At the moment its not as-documented or as the kernel is using those numbers. I assume this is something that changed in resctrl when it was merged, and this selftest tool just needs updating. Thanks, James [0] https://lkml.org/lkml/2019/2/9/384
