Messages in this thread | | | Date | Wed, 26 Feb 2020 17:19:41 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 1/2] kstats: kernel metric collector |
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On Wed, Feb 26, 2020 at 05:46:36AM -0800, Luigi Rizzo wrote: > kstats is a helper to accumulate in-kernel metrics (timestamps, sizes, > etc.) and show distributions through debugfs. > Set CONFIG_KSTATS=m or y to enable it. > > Creating a metric takes one line of code (and one to destroy it): > > struct kstats *key = kstats_new("foo", 3 /* frac_bits */); > ... > kstats_delete(key); > > The following line records a u64 sample: > > kstats_record(key, value); > > kstats_record() is cheap (5ns hot cache, 250ns cold cache). Samples are > accumulated in a per-cpu array with 2^frac_bits slots for each power > of 2. Using frac_bits = 3 gives about 30 slots per decade.
So I think everybody + dog has written code like this, although I never bothered with the log2 based buckets myself. Nor have I ever bothered with doing a debugfs interface.
I find it very hard to convince myself something like this deserves to live upstream, vs. remaining in the local debug/hack toolbox.
Tracing has an aggregator (histogram), you can dump the raw deltas, or you can hack up a custom aggregator in a few lines, or you do BPF if you're so inclined.
Why do we need this specific one?
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