Hi Tejun, Thanks for taking the time to read my proposal! Sorry for the late reply. This email skipped my inbox for some reason. On Sun, Mar 13, 2022 at 10:35 PM Tejun Heo <tj@xxxxxxxxxx> wrote: > > Hello, > > On Wed, Mar 09, 2022 at 12:27:15PM -0800, Yosry Ahmed wrote: > ... > > These problems are already addressed by the rstat aggregation > > mechanism in the kernel, which is primarily used for memcg stats. We > > Not that it matters all that much but I don't think the above statement is > true given that sched stats are an integrated part of the rstat > implementation and io was converted before memcg. > Excuse my ignorance, I am new to kernel development. I only saw calls to cgroup_rstat_updated() in memcg and io and assumed they were the only users. Now I found cpu_account_cputime() :) > > - For every cgroup, we will either use flags to distinguish BPF stats > > updates from normal stats updates, or flush both anyway (memcg stats > > are periodically flushed anyway). > > I'd just keep them together. Usually most activities tend to happen > together, so it's cheaper to aggregate all of them in one go in most cases. This makes sense to me, thanks. > > > - Provide flags to enable/disable using per-cpu arrays (for stats that > > are not updated frequently), and enable/disable hierarchical > > aggregation (for non-hierarchical stats, they can still make benefit > > of the automatic entries creation & deletion). > > - Provide different hierarchical aggregation operations : SUM, MAX, MIN, etc. > > - Instead of an array as the map value, use a struct, and let the user > > provide an aggregator function in the form of a BPF program. > > I'm more partial to the last option. It does make the usage a bit more > compilcated but hopefully it shouldn't be too bad with good examples. > > I don't have strong opinions on the bpf side of things but it'd be great to > be able to use rstat from bpf. It indeed gives more flexibility but is more complicated. Also, I am not sure about the overhead to make calls to BPF programs in every aggregation step. Looking forward to get feedback on the bpf side of things. > > Thanks. > > -- > tejun
