On Thu, May 28, 2020 at 06:39:08PM -0700, Axel Rasmussen wrote: > The use case we have in mind for this is to enable this instrumentation > widely in Google's production fleet. Internally, we have a userspace thing > which scrapes these metrics and publishes them such that we can look at > aggregate metrics across our fleet. The thinking is that mechanisms like > lockdep or getting histograms with e.g. BPF attached to the tracepoint > introduces too much overhead for this to be viable. (Although, granted, I > don't have benchmarks to prove this - if there's skepticism, I can produce > such a thing - or prove myself wrong and rethink my approach. :) ) Whichever way around; I don't believe in special instrumentation like this. We'll grow a thousand separate pieces of crap if we go this route. Next on, someone will come and instrument yet another lock, with yet another 1000 lines of gunk. Why can't you kprobe the mmap_lock things and use ftrace histograms?
