On Wed, 27 Jan 2021 11:32:08 GMT, djelinski <github.com+30433125+djelin...@openjdk.org> wrote:
> Under certain load, MemoryCache operations take a substantial fraction of the > time needed to complete SSL handshakes. This series of patches improves > performance characteristics of MemoryCache, at the cost of a functional > change: expired entries are no longer guaranteed to be removed before live > ones. Unused entries are still removed before used ones, and cache > performance no longer depends on its capacity. > > First patch in the series contains a benchmark that can be run with `make > test TEST="micro:CacheBench"`. > Baseline results before any MemoryCache changes: > Benchmark (size) (timeout) Mode Cnt Score Error Units > CacheBench.put 20480 86400 avgt 25 83.653 ? 6.269 us/op > CacheBench.put 20480 0 avgt 25 0.107 ? 0.001 us/op > CacheBench.put 204800 86400 avgt 25 2057.781 ? 35.942 us/op > CacheBench.put 204800 0 avgt 25 0.108 ? 0.001 us/op > there's a nonlinear performance drop between 20480 and 204800 entries, > probably attributable to CPU cache thrashing. Beyond 204800 entries the cache > scales more linearly. > > Benchmark results after the 2nd and 3rd patches are pretty similar, so I'll > only copy one: > Benchmark (size) (timeout) Mode Cnt Score Error Units > CacheBench.put 20480 86400 avgt 25 0.146 ? 0.002 us/op > CacheBench.put 20480 0 avgt 25 0.108 ? 0.002 us/op > CacheBench.put 204800 86400 avgt 25 0.150 ? 0.001 us/op > CacheBench.put 204800 0 avgt 25 0.106 ? 0.001 us/op > The third patch improves worst-case times on a mostly idle cache by > scattering removal of expired entries over multiple `put` calls. It does not > affect performance of an overloaded cache. > > The 4th patch removes all code that clears cached values before handing them > over to the GC. [This > comment](https://github.com/openjdk/jdk/commit/5859a0320334bfb6b46b62eb16b4c387641f4a2a#diff-c6bd583a97fbc4f471621fee7eab37c63718cdb6932ce357fa403cfda4b32b6fL346) > stated that clearing values was supposed to be a GC performance > optimization. It wasn't. Benchmark results after that commit: > Benchmark (size) (timeout) Mode Cnt Score Error Units > CacheBench.put 20480 86400 avgt 25 0.113 ? 0.001 us/op > CacheBench.put 20480 0 avgt 25 0.075 ? 0.002 us/op > CacheBench.put 204800 86400 avgt 25 0.116 ? 0.001 us/op > CacheBench.put 204800 0 avgt 25 0.072 ? 0.001 us/op > I wasn't expecting that much of an improvement, and don't know how to explain > it. > > The 40ns difference between cache with and without a timeout can be > attributed to 2 `System.currentTimeMillis()` calls; they were pretty slow on > my VM. make/test/BuildMicrobenchmark.gmk line 97: > 95: SRC := $(MICROBENCHMARK_SRC), \ > 96: BIN := $(MICROBENCHMARK_CLASSES), \ > 97: JAVAC_FLAGS := $(JAVAC_FLAGS) --add-exports > java.base/sun.security.util=ALL-UNNAMED, \ Why do you need to add $(JAVAC_FLAGS) here? ------------- PR: https://git.openjdk.java.net/jdk/pull/2255
