Request for reviews (M): 7079329: Adjust allocation prefetching for T4

[Vladimir Kozlov]

On 8/16/11 2:29 AM, Christian Thalinger wrote:
>
> On Aug 16, 2011, at 3:12 AM, Vladimir Kozlov wrote:
>
>> http://cr.openjdk.java.net/~kvn/7079329/webrev
>>
>> 7079329: Adjust allocation prefetching for T4
>>
>> L2 cache line size is 32 bytes on T4 instead of 64 bytes on T series before. As result BIS instruction prefetches only 32 bytes. Jbb2005 runs show that prefetching 64 bytes is still better on T4 so 2 BIS instructions should be issued.
>>
>> BIS can't be use for general prefetching since it may fault. New PrefetchAllocation node was added for allocation prefetching.
>>
>> Changed prefetchAlloc_bis parameter from memory to regP.
>>
>> Use AllocatePrefetchInstr on Sparc to allow specify what instruction to use for allocation prefetching (0: prefetch write, 1: BIS).
>>
>> Added new instructions on Sparc cacheLineAdrX to reduce number of instructions generated for finding next cache line address.
>>
>> Added new flag AllocateInstPrefetchLines to specify number of lines to prefetch for instance allocation.
>>
>> L1_data_cache_line_size() renamed to prefetch_data_size().
>
> src/cpu/x86/vm/x86_32.ad:
> src/cpu/x86/vm/x86_64.ad:
>
> Can you use MacroAssembler instructions to emit the code for the new instructs?

OK.

>
> src/cpu/sparc/vm/vm_version_sparc.cpp:
>
> +       if (is_T4()) {
> +         // Double number of prefetched cache lines on T4
> +         // since L2 cache line size is smaller (32 bytes).
> +         if (FLAG_IS_DEFAULT(AllocatePrefetchLines)) {
> +           FLAG_SET_DEFAULT(AllocatePrefetchLines, 6);
> +         }
> +         if (FLAG_IS_DEFAULT(AllocateInstPrefetchLines)) {
> +           FLAG_SET_DEFAULT(AllocateInstPrefetchLines, 2);
> +         }
> +       }
>
> Maybe you should use *2 here.

Something like this?:

+         if (FLAG_IS_DEFAULT(AllocatePrefetchLines)) {
+           FLAG_SET_DEFAULT(AllocatePrefetchLines, AllocatePrefetchLines*2);
+         }

Vladimir

>
> Otherwise this looks good.
>
> -- Christian