On 14/05/20 19:35, Jonathan Adams wrote: >> In general for statsfs we took a more explicit approach where each >> addend in a sum is a separate stats_fs_source. In this version of the >> patches it's also a directory, but we'll take your feedback and add both >> the ability to hide directories (first) and to list values (second). >> >> So, in the cases of interfaces and KVM objects I would prefer to keep >> each addend separate. > > This just feels like a lot of churn just to add a statistic or object; > in your model, every time a KVM or VCPU is created, you create the N > statistics, leading to N*M total objects. While it's N*M files, only O(M) statsfs API calls are needed to create them. Whether you have O(N*M) total kmalloc-ed objects or O(M) is an implementation detail. Having O(N*M) API calls would be a non-started, I agree - especially once you start thinking of more efficient publishing mechanisms that unlike files are also O(M). >> For CPUs that however would be pretty bad. Many subsystems might >> accumulate stats percpu for performance reason, which would then be >> exposed as the sum (usually). So yeah, native handling of percpu values >> makes sense. I think it should fit naturally into the same custom >> aggregation framework as hash table keys, we'll see if there's any devil >> in the details. >> >> Core kernel stats such as /proc/interrupts or /proc/stat are the >> exception here, since individual per-CPU values can be vital for >> debugging. For those, creating a source per stat, possibly on-the-fly >> at hotplug/hot-unplug time because NR_CPUS can be huge, would still be >> my preferred way to do it. > > Our metricfs has basically two modes: report all per-CPU values (for > the IPI counts etc; you pass a callback which takes a 'int cpu' > argument) or a callback that sums over CPUs and reports the full > value. It also seems hard to have any subsystem with a per-CPU stat > having to install a hotplug callback to add/remove statistics. Yes, this is also why I think percpu values should have some kind of native handling. Reporting per-CPU values individually is the exception. > In my model, a "CPU" parameter enum which is automatically kept > up-to-date is probably sufficient for the "report all per-CPU values". Yes (or a separate CPU source in my model). Paolo > Does this make sense to you? I realize that this is a significant > change to the model y'all are starting with; I'm willing to do the > work to flesh it out. > Thanks for your time, > - Jonathan > > P.S. Here's a summary of the types of statistics we use in metricfs > in google, to give a little context: > > - integer values (single value per stat, source also a single value); > a couple of these are boolean values exported as '0' or '1'. > - per-CPU integer values, reported as a <cpuid, value> table > - per-CPU integer values, summed and reported as an aggregate > - single-value values, keys related to objects: > - many per-device (disk, network, etc) integer stats > - some per-device string data (version strings, UUIDs, and > occasional statuses.) > - a few histograms (usually counts by duration ranges) > - the "function name" to count for the WARN statistic I mentioned. > - A single statistic with two keys (for livepatch statistics; the > value is the livepatch status as a string) > > Most of the stats with keys are "complete" (every key has a value), > but there are several examples of statistics where only some of the > possible keys have values, or (e.g. for networking statistics) only > the keys visible to the reading process (e.g. in its namespaces) are > included. >
