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To make it clear we may have to print all the CLOSes in each domain. >>> >>> Could you please elaborate how this is confusing? >> >> # cat /sys/fs/resctrl/info/L3/bit_usage >> 0=HHHHXXXXSSSS0000 >> >> This may give the impression that the all CLOSes in all domains carries >> this property, but in reality, it applies only to one CLOS(15) within each >> domain. >> >> Example below.... >> > > ... > >> Here is the behaviour after these cahnges. >> >> === Before io_alloc enabled============================== >> >> #cd /sys/fs/resctrl/L3/ >> # cat io_alloc >> disabled >> >> # cat shareable_bits >> 0 (This is always 0 for AMD) >> >> # cat bit_usage >> 0=SSSSSSSSSSSSSSSS;1=SSSSSSSSSSSSSSSS;2=SSSSSSSSSSSSSSSS;3=SSSSSSSSSSSSSSSS > > Please note that the "S" in above does not have anything to do with > "shareable_bits" at this point. The "S" indicates that all L3 instances > are currently used by software and that sharing is allowed. > > "bit_usage" gives insight to user space how all L3 instances are used. > > If at this point a new resource group is created and it has an "exclusive" > allocation then "bit_usage" will change to reflect that. For example, > you can try this on the system you are testing on: > > # echo 'L3:0=fff0;1=fff0;2=fff0;3=fff0' > /sys/fs/resctrl/schemata > # mkdir /sys/fs/resctrl/g1 > # echo 'L3:0=f;1=f;2=f;3=f' > /sys/fs/resctrl/g1/schemata > # echo 'exclusive' > /sys/fs/resctrl/g1/mode > > The above isolates a portion of all L3 instances for exclusive use by g1. > After above changes: > # cat /sys/fs/resctrl/info/L3/bit_usage > 0=SSSSSSSSSSSSEEEE;1=SSSSSSSSSSSSEEEE;2=SSSSSSSSSSSSEEEE;3=SSSSSSSSSSSSEEEE > Yes. I see the same output. > Note that there is no "closid" or resource group information but instead, > "bit_usage" shows to user space how each cache instance is being used > across all resource groups and hardware (IO) allocations. Ok. Got it. > >> >> ==== After io_alloc enabled================================= >> >> # echo 1 > io_alloc >> >> # cat io_alloc >> enabled >> >> # cat io_alloc_cbm >> L3:0=ffff;1=ffff;2=ffff;3=ffff >> >> #cat bit_usage >> 0=XXXXXXXXXXXXXXXX;1=XXXXXXXXXXXXXXXX;2=XXXXXXXXXXXXXXXX;3=XXXXXXXXXXXXXXXX > > Looks accurate to me. It shows that both hardware and software can > allocate into all portions of all caches. > >> >> ==== After changing io_alloc_cbm ============================ >> >> #echo "L3:0=ff00;1=ff00;2=ff00;3=ff00 > io_alloc_cbm >> >> # cat io_alloc_cbm >> L3:0=ff00;1=ff00;2=ff00;3=ff00 >> >> #cat bit_usage >> 0=XXXXXXXXSSSSSSSS;1=XXXXXXXXSSSSSSSS;2=XXXXXXXXSSSSSSSS;3=XXXXXXXXSSSSSSSS > > Looks accurate to me. > >> ============================================================= >> >> My concern here is, this may imply that the property is present across all >> CLOSes in all the domains, while in fact, it only applies to a single >> CLOS(15) within each domain. > > If a user wants a resource group specific view then the schemata should be used. > "bit_usage" presents the view from the cache instance perspective and reflects > how each L3 cache instance is being used at that moment in time. It helps > system administrator answer the question "how are the caches used at the moment"? > "bit_usage" does so by presenting a summary of all allocations across all resource > groups and any hardware allocations that may exist. This file helps user space > to understand how the cache is being used without needing to correlate the CBMs > of all resource groups and IO allocations. For example, "bit_usage" is to be used > by system administrator to ensure cache is used optimally (for example, there are > no unused portions). Also, a user may be investigating a performance issue in > a particular resource group and "bit_usage" will help with that to see if > the tasks in that resource group may be competing with IO. > Ok, "bit_usage" is a summary across all the groups. That is a good point. Thanks for the detailed explanation. Will make those changes in next revision. Thank you. Babu