RFR: 8276618: Pad cacheline for Thread::_rcu_counter

[Hamlin Li]

On Thu, 4 Nov 2021 05:09:48 GMT, Hamlin Li <mli at openjdk.org> wrote:

> Currently, Thread::_rcu_counter is not padded by cacheline, it should be beneficail to do so.
> 
> The initial spebjbb test shows about 10.5% improvement of critical, and 0.7% improvement of max in specjbb2015.
> 
> 
> 
> ========= test result (1st round) ==========
> rcu		base
> 45096		38980
> 41741		41468
> 42349		41053
> 44485		42030
> 47103		39915
> 43864		36004
> 
> ==== average ====
> 44106.33333		39908.33333
> 
> ==== improvement ====
> 10.5%
> 
> ========= test result (2nd round) ==========
> Second round of run includes 3 types: 
> 1. pad gc data & pad rcu
> 2. pad rcu only
> 3. base
> 
> Although the improvement is not that much as the previous round (10%), but still got about 3~4% improvement.
> 
> gc data + rcu	rcu	base
> 41284	41860	37099
> 42296	42166	44692
> 42810	43423	41801
> 43492	45603	40274
> 43808	40641	39627
> 43029	40242	39793
> 42543	41662	41544
> 43420	42702	37991
> 44212	43354	40319
> 42692	43442	45264
> 44773	44577	44213
> 40835	41870	42008
> 44282	44167	42527
> 
> ==== average ====
> 43036.61538	42746.84615	41319.38462
> 
> ==== improvement ====
> gc data + rcu / base: 4.156%
> rcu / base: 3.45%
> 
> 
> 
> 
> ========= configuration and environment ==========
> specjbb arguments:
>   GROUP_COUNT=4
>   TI_JVM_COUNT=1
> 
>   SPEC_OPTS_C="-Dspecjbb.group.count=$GROUP_COUNT -Dspecjbb.txi.pergroup.count=$TI_JVM_COUNT"
>   SPEC_OPTS_TI=""
>   SPEC_OPTS_BE=""
> 
>   JAVA_OPTS_C="-server -Xms2g -Xmx2g -XX:+UseParallelGC"
>   JAVA_OPTS_TI="-server -Xms2g -Xmx2g -XX:+UseParallelGC"
>   JAVA_OPTS_BE="-server -XX:+UseG1GC -Xms32g -Xmx32g"
> 
>   MODE_ARGS_C="-ikv"
>   MODE_ARGS_TI="-ikv"
>   MODE_ARGS_BE="-ikv"
> 
>   NUM_OF_RUNS=1
> 
> HW:
>   Architecture:        x86_64
>   CPU op-mode(s):      32-bit, 64-bit
>   Byte Order:          Little Endian
>   CPU(s):              224
>   On-line CPU(s) list: 0-223
>   Thread(s) per core:  2
>   Core(s) per socket:  28
>   Socket(s):           4
>   NUMA node(s):        4
>   Vendor ID:           GenuineIntel
>   CPU family:          6
>   Model:               85
>   Model name:          Intel(R) Xeon(R) Platinum 8176M CPU @ 2.10GHz
>   Stepping:            4
>   CPU MHz:             1001.925
>   CPU max MHz:         2101.0000
>   CPU min MHz:         1000.0000
>   BogoMIPS:            4200.00
>   Virtualization:      VT-x
>   L1d cache:           32K
>   L1i cache:           32K
>   L2 cache:            1024K
>   L3 cache:            39424K
>   NUMA node0 CPU(s):   0-27,112-139
>   NUMA node1 CPU(s):   28-55,140-167
>   NUMA node2 CPU(s):   56-83,168-195
>   NUMA node3 CPU(s):   84-111,196-223
> 
>               total        used        free      shared  buff/cache   available
> Mem:           3.0T        3.8G        2.9T         18M         25G        2.9T
> Swap:           99G          0B         99G

Thanks Thomas for the feedback.

I have updated the summary of this PR with more configuration and environment info, and I also updated the 2nd round of run. Although the improvement is not that much as the previous round (10%), but still got about 3~4% improvement, and seems the data is more stable than the 1st round of run.
(JBS is not available currently, will update JBS too later)

-------------

PR: https://git.openjdk.java.net/jdk/pull/6246