truffle: src/share/vm/code/nmethod.cpp comparison

comparison src/share/vm/code/nmethod.cpp @ 2339:3d5a546351ef

7023931: PcDescCache::find_pc_desc should not write _last_pc_desc Summary: Remove _last_pc_desc and use pcdescs[0] instead. Reviewed-by: dcubed, coleenp, ysr

author	phh
date	Fri, 11 Mar 2011 16:09:55 -0500
parents	1b4e6a5d98e0
children	65f880e2869b

comparison

equal deleted inserted replaced

-:4f148718983e
+:3d5a546351ef
 }
 int pc_desc_resets;   // number of resets (= number of caches)
 int pc_desc_queries;  // queries to nmethod::find_pc_desc
 int pc_desc_approx;   // number of those which have approximate true
-int pc_desc_repeats;  // number of _last_pc_desc hits
+int pc_desc_repeats;  // number of _pc_descs[0] hits
 int pc_desc_hits;     // number of LRU cache hits
 int pc_desc_tests;    // total number of PcDesc examinations
 int pc_desc_searches; // total number of quasi-binary search steps
 int pc_desc_adds;     // number of LUR cache insertions
 return (pc-1)->pc_offset() < pc_offset && pc_offset <= pc->pc_offset();
 }
 void PcDescCache::reset_to(PcDesc* initial_pc_desc) {
 if (initial_pc_desc == NULL) {
-_last_pc_desc = NULL;  // native method
+_pc_descs[0] = NULL; // native method; no PcDescs at all
 return;
 }
 NOT_PRODUCT(++nmethod_stats.pc_desc_resets);
 // reset the cache by filling it with benign (non-null) values
 assert(initial_pc_desc->pc_offset() < 0, "must be sentinel");
-_last_pc_desc = initial_pc_desc + 1;  // first valid one is after sentinel
 for (int i = 0; i < cache_size; i++)
 _pc_descs[i] = initial_pc_desc;
 }
 PcDesc* PcDescCache::find_pc_desc(int pc_offset, bool approximate) {
 NOT_PRODUCT(++nmethod_stats.pc_desc_queries);
-NOT_PRODUCT(if (approximate)  ++nmethod_stats.pc_desc_approx);
+NOT_PRODUCT(if (approximate) ++nmethod_stats.pc_desc_approx);
+// Note: one might think that caching the most recently
+// read value separately would be a win, but one would be
+// wrong.  When many threads are updating it, the cache
+// line it's in would bounce between caches, negating
+// any benefit.
 // In order to prevent race conditions do not load cache elements
 // repeatedly, but use a local copy:
 PcDesc* res;
-// Step one:  Check the most recently returned value.
+// Step one:  Check the most recently added value.
-res = _last_pc_desc;
+res = _pc_descs[0];
-if (res == NULL)  return NULL;  // native method; no PcDescs at all
+if (res == NULL) return NULL;  // native method; no PcDescs at all
 if (match_desc(res, pc_offset, approximate)) {
 NOT_PRODUCT(++nmethod_stats.pc_desc_repeats);
 return res;
 }
-// Step two:  Check the LRU cache.
+// Step two:  Check the rest of the LRU cache.
-for (int i = 0; i < cache_size; i++) {
+for (int i = 1; i < cache_size; ++i) {
 res = _pc_descs[i];
-if (res->pc_offset() < 0)  break;  // optimization: skip empty cache
+if (res->pc_offset() < 0) break;  // optimization: skip empty cache
 if (match_desc(res, pc_offset, approximate)) {
 NOT_PRODUCT(++nmethod_stats.pc_desc_hits);
-_last_pc_desc = res;  // record this cache hit in case of repeat
 return res;
 }
 }
 // Report failure.
 return NULL;
 }
 void PcDescCache::add_pc_desc(PcDesc* pc_desc) {
 NOT_PRODUCT(++nmethod_stats.pc_desc_adds);
-// Update the LRU cache by shifting pc_desc forward:
+// Update the LRU cache by shifting pc_desc forward.
 for (int i = 0; i < cache_size; i++)  {
 PcDesc* next = _pc_descs[i];
 _pc_descs[i] = pc_desc;
 pc_desc = next;
 }
-// Note:  Do not update _last_pc_desc.  It fronts for the LRU cache.
 }
 // adjust pcs_size so that it is a multiple of both oopSize and
 // sizeof(PcDesc) (assumes that if sizeof(PcDesc) is not a multiple
 // of oopSize, then 2*sizeof(PcDesc) is)
-static int  adjust_pcs_size(int pcs_size) {
+static int adjust_pcs_size(int pcs_size) {
 int nsize = round_to(pcs_size,   oopSize);
 if ((nsize % sizeof(PcDesc)) != 0) {
 nsize = pcs_size + sizeof(PcDesc);
 }
-assert((nsize %  oopSize) == 0, "correct alignment");
+assert((nsize % oopSize) == 0, "correct alignment");
 return nsize;
 }
 //-----------------------------------------------------------------------------

Mercurial > hg > truffle

comparison src/share/vm/code/nmethod.cpp @ 2339:3d5a546351ef