Messages in this thread | | | Date | Tue, 23 Aug 2022 10:09:53 -0700 | Subject | Re: [PATCH v5 00/21] x86/resctrl: Make resctrl_arch_rmid_read() return values in bytes | From | Reinette Chatre <> |
| |
Hi,
On 7/3/2022 8:54 AM, Xin Hao wrote: > Hi james, > > I have a review all of the patches, it looks goot to me, but i also test them once again, i have a little confusion with my test. > > # mkdir p1 > > # echo "L3:0=001;1=001" > p1/schemata > > # [root@iZbp1bu26qv0j3ddyusot3Z p1]# cat schemata > MB:0=100;1=100 > L3:0=001;1=001 > > # memhog -r1000000 1000m > /mnt/log & > > [1] 53023 > [root@iZbp1bu26qv0j3ddyusot3Z p1]# echo 53023 > tasks > [ > [root@iZbp1bu26qv0j3ddyusot3Z p1]# cat mon_data/mon_L3_00/llc_occupancy > 3833856 > [root@iZbp1bu26qv0j3ddyusot3Z p1]# cat mon_data/mon_L3_00/llc_occupancy > 3620864 > [root@iZbp1bu26qv0j3ddyusot3Z p1]# cat mon_data/mon_L3_00/llc_occupancy > 3727360 > [root@iZbp1bu26qv0j3ddyusot3Z p1]# cat size > MB:0=100;1=100 > L3:0=3407872;1=3407872 > > Obviously, the value has been overflowed, Can you explain why?
Are you seeing different behavior before and after you apply this series?
I do not think the conclusion should immediately be that there is an overflow issue. Have you perhaps run into the scenario "Notes on cache occupancy monitoring and control" described in Documentation/x86/resctrl.rst?
When "memhog" starts it can allocate to the entire L3 for a while before it is moved to the constrained resource group. It's cache lines are not evicted as part of this move so it is not unusual for it to have more lines in L3 than it is allowed to allocate into.
Understanding the occupancy values require understanding of the workload as well as the system environment.
Depending on the workload's data usage (for example if it keeps loading new data - note that if the workload keeps loading the same data and the data is already present in an area of cache that the workload cannot allocate into then the data read would still result in a cache hit for the workload, the data would not be moved to the area the workload can allocate into) and other workloads on the system (there is other load present also that evicts the lines owned by the workload) the L3 occupancy rate should go down after a while to match the space it can allocate into.
Reinette
| |