Axel, Axel Rasmussen <axelrasmussen@xxxxxxxxxx> writes: > The overall goal of this patchset is to add a latency histogram which measures > `mmap_lock` acquisition time. This is useful to measure the impact of ongoing > work like maple trees and range locks (https://lwn.net/Articles/787629/), and > it is also useful to debug userspace processes which experience long waits due > to lock contention. > > This patchset is built upon walken@xxxxxxxxxx's new `mmap_lock` API > (https://lkml.org/lkml/2020/4/21/1307). In its current form, it should apply > cleanly to a 5.7-rc7 tree to which Michel's patchset has already been applied. > > To summarize the changes being made at a high level: > > - Add a histogram library: a `struct histogram` is effectively an array of > thresholds (i.e., buckets), and an array of per-cpu `u64` counts of the > number of samples in each bucket. this is maybe a redundant question as I did not follow the V1 submission. Why do we need yet another histogram mechanism for instrumentation purposes? ftrace has histogram support already. Why can't this be reused? Thanks, tglx
