JDK 9 RFR of 6375303: Review use of caching in BigDecimal (original) (raw)

Peter Levart peter.levart at gmail.com
Mon Mar 24 09:21:55 UTC 2014

On 03/20/2014 08:49 AM, Aleksey Shipilev wrote:

On 03/20/2014 11:06 AM, Peter Levart wrote:

I was thinking about last night, for question: "Why is this double-checked non-volatile-then-volatile trick not any faster than pure volatile variant even on ARM platform where volatile read should have some penalty compared to normal read?", might be in the fact that Raspberry Pi is a single-core/single-thread "machine". Would anyone with JVM JIT compiler expertise care to share some insight? I suspect that on such platform, the compiler optimizes volatile accesses so that they are performed without otherwise necessary memory fences... Yes, at least C2 is known to not emit memory fences on uniprocessor machines. You need to have a multicore ARM. If you are still interested, contact me privately and I can arrange the access to my personal quad-core Cortex-A9. -Aleksey.

Hi,

Thanks to Aleksey for re-establishing the access, I bring you results of the microbenchmark from his quad-core Cortex-A9:

JDK 8 options: -client, org.openjdk.jmh.Main parameters: ".*" -i 10 -r 5 -wi 5 -w 1 -f 1 [-t 1|max]

--- Baseline, 1-thread ---

Benchmark Mode Samples Mean Mean error Units o.t.Bench6375303.testFirstToString avgt 10 69292.305 299.516 ns/op o.t.Bench6375303.testToString avgt 1020.003 0.433 ns/op

--- Baseline, 4-threads ---

Benchmark Mode Samples Mean Mean error Units o.t.Bench6375303.testFirstToString avgt 10 100390.024 2158.132 ns/op o.t.Bench6375303.testToString avgt 1020.151 0.677 ns/op

--- double-checked nonvolatile-then-volatile-read+CAS, 1-thread ---

Benchmark Mode Samples Mean Mean error Units o.t.Bench6375303.testFirstToString avgt 10 69951.406 221.516 ns/op o.t.Bench6375303.testToString avgt 1019.681 0.025 ns/op

--- double-checked nonvolatile-then-volatile-read+CAS, 4-threads ---

Benchmark Mode Samples Mean Mean error Units o.t.Bench6375303.testFirstToString avgt 10 104231.335 3842.095 ns/op o.t.Bench6375303.testToString avgt 1020.030 0.595 ns/op

--- classic volatile read+CAS, 1-thread ---

Benchmark Mode Samples Mean Mean error Units o.t.Bench6375303.testFirstToString avgt 10 69753.542 180.110 ns/op o.t.Bench6375303.testToString avgt 1023.285 0.267 ns/op

--- classic volatile read+CAS, 4-threads ---

Benchmark Mode Samples Mean Mean error Units o.t.Bench6375303.testFirstToString avgt 10 99664.256 1814.090 ns/op o.t.Bench6375303.testToString avgt 1023.491 0.606 ns/op

...as can be seen, the double-checked read-then-volatile-read+CAS trick is about 15% faster than classic volatile-read+CAS in this case.

Regards, Peter

More information about the core-libs-dev mailing list