RFR: 8281936: compiler/arguments/TestCodeEntryAlignment.java fails on AVX512 machines [v2]

[Jie Fu]

On Thu, 17 Feb 2022 19:46:03 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> I would like to hear explanation why the test failed with `-XX:CodeEntryAlignment=16` on avx512 when it passed with bigger default value 32 (or other bigger values):
> https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/globals_x86.hpp#L47

Let's see the code buffer size after line 3005 with CodeEntryAlignment={16, 32, 64}

2999 RuntimeStub* SharedRuntime::generate_resolve_blob(address destination, const char* name) {
3000   assert (StubRoutines::forward_exception_entry() != NULL, "must be generated before");
3001
3002   // allocate space for the code
3003   ResourceMark rm;
3004
3005   CodeBuffer buffer(name, 1000, 512);
3006   MacroAssembler* masm                = new MacroAssembler(&buffer);
3007
3008   int frame_size_in_words;


The `insts.code` is only 1128 for `CodeEntryAlignment=16` which is not enough on AVX512.

CodeEntryAlignment=16

CodeBuffer:
  consts.code = 0x0000000000000000 : 0x0000000000000000 : 0x0000000000000000 (0 of 0)
  consts.locs = 0x0000000000000000 : 0x0000000000000000 : 0x0000000000000000 (0 of 0) point=0
   insts.code = 0x00007fffd90adc90 : 0x00007fffd90adc90 : 0x00007fffd90ae0f8 (0 of 1128)
   insts.locs = 0x00007ffff0027098 : 0x00007ffff0027098 : 0x00007ffff0027298 (0 of 256) point=0
   stubs.code = 0x0000000000000000 : 0x0000000000000000 : 0x0000000000000000 (0 of 0)
   stubs.locs = 0x0000000000000000 : 0x0000000000000000 : 0x0000000000000000 (0 of 0) point=0


CodeEntryAlignment=32

CodeBuffer:
  consts.code = 0x0000000000000000 : 0x0000000000000000 : 0x0000000000000000 (0 of 0)
  consts.locs = 0x0000000000000000 : 0x0000000000000000 : 0x0000000000000000 (0 of 0) point=0
   insts.code = 0x00007fffd90add20 : 0x00007fffd90add20 : 0x00007fffd90ae208 (0 of 1256)
   insts.locs = 0x00007ffff0027098 : 0x00007ffff0027098 : 0x00007ffff0027298 (0 of 256) point=0
   stubs.code = 0x0000000000000000 : 0x0000000000000000 : 0x0000000000000000 (0 of 0)
   stubs.locs = 0x0000000000000000 : 0x0000000000000000 : 0x0000000000000000 (0 of 0) point=0


CodeEntryAlignment=64

CodeBuffer:
  consts.code = 0x0000000000000000 : 0x0000000000000000 : 0x0000000000000000 (0 of 0)
  consts.locs = 0x0000000000000000 : 0x0000000000000000 : 0x0000000000000000 (0 of 0) point=0
   insts.code = 0x00007fffd90adec0 : 0x00007fffd90adec0 : 0x00007fffd90ae4a8 (0 of 1512)
   insts.locs = 0x00007ffff0027098 : 0x00007ffff0027098 : 0x00007ffff0027298 (0 of 256) point=0
   stubs.code = 0x0000000000000000 : 0x0000000000000000 : 0x0000000000000000 (0 of 0)
   stubs.locs = 0x0000000000000000 : 0x0000000000000000 : 0x0000000000000000 (0 of 0) point=0



The related code logic at line 100 & 105, which shows larger `insts.code` with higher `CodeEntryAlignment`.

  98 void CodeBuffer::initialize(csize_t code_size, csize_t locs_size) {
  99   // Compute maximal alignment.
 100   int align = _insts.alignment();                     // <--- will return CodeEntryAlignment
 101   // Always allow for empty slop around each section.
 102   int slop = (int) CodeSection::end_slop();
 103
 104   assert(blob() == NULL, "only once");
 105   set_blob(BufferBlob::create(_name, code_size + (align+slop) * (SECT_LIMIT+1)));

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PR: https://git.openjdk.java.net/jdk/pull/7485