RFR: 8259886 : Improve SSL session cache performance and scalability [v3]
djelinski
github.com+30433125+djelinski at openjdk.java.net
Thu Feb 4 19:16:59 UTC 2021
> 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.
djelinski has updated the pull request incrementally with one additional commit since the last revision:
Add benchmarks for get and remove
-------------
Changes:
- all: https://git.openjdk.java.net/jdk/pull/2255/files
- new: https://git.openjdk.java.net/jdk/pull/2255/files/34949970..abe0e238
Webrevs:
- full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2255&range=02
- incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2255&range=01-02
Stats: 76 lines in 1 file changed: 54 ins; 4 del; 18 mod
Patch: https://git.openjdk.java.net/jdk/pull/2255.diff
Fetch: git fetch https://git.openjdk.java.net/jdk pull/2255/head:pull/2255
PR: https://git.openjdk.java.net/jdk/pull/2255
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