[9] RFR (S) 8157184: java/lang/invoke/LFCaching/LFMultiThreadCachingTest.java failed with a fatal error

Vladimir Kozlov vladimir.kozlov at oracle.com
Thu May 19 17:18:29 UTC 2016



Here is possible failure scenario:

PICL is not installed on the failed SPARC machine as result 
_L2_data_cache_line_size is 0 (unknown). In such situation we should not 
use BIS instructions. But AllocatePrefetchInstr setting is not guarded 
by cache_line_size > 0 check and BIS instruction is selected:

The default value for AllocatePrefetchStepSize is 16 when 
cache_line_size is 0 which is smaller then real cache line size (32).

Flags values on crashing T5 machine:
Reserve for allocation:        24
AllocatePrefetchLines:         6
AllocateInstancePrefetchLines: 2
AllocatePrefetchDistance:      64
AllocatePrefetchStepSize:      16
AllocatePrefetchInstr:         1
AllocatePrefetchStyle:         3

_reserve_for_allocation_prefetch = (AllocatePrefetchDistance + 
AllocatePrefetchStepSize * lines)

It is not multiply of real cache line size since 
AllocatePrefetchStepSize =16 < 32 bytes cache line on T5.

And since we are using BIS instruction it can clean whole cache line if 
it is executed for address aligned to the start of cache line and at the 
end of reserved space: _reserve_for_allocation_prefetch -16. As result 
it may clear values after reserved space (in following TLAB).

Solution: add missing cache_line_size > 0 checks.

Tested comp and jdk:tier1+tier2 RBT and forced _L2_data_cache_line_size = 0.


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