diff --git a/src/share/vm/code/nmethod.cpp b/src/share/vm/code/nmethod.cpp index b75569b54a677436bc501aad5ecaa45033d56ccc..b9211b9aa111566dcd0167cf341066d5e506daa5 100644 --- a/src/share/vm/code/nmethod.cpp +++ b/src/share/vm/code/nmethod.cpp @@ -170,7 +170,7 @@ struct nmethod_stats_struct { 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 @@ -278,40 +278,44 @@ static inline bool match_desc(PcDesc* pc, int pc_offset, bool approximate) { 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. - res = _last_pc_desc; - if (res == NULL) return NULL; // native method; no PcDescs at all + // Step one: Check the most recently added value. + res = _pc_descs[0]; + 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. - for (int i = 0; i < cache_size; i++) { + // Step two: Check the rest of the LRU cache. + 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; } } @@ -322,24 +326,23 @@ PcDesc* PcDescCache::find_pc_desc(int pc_offset, bool approximate) { 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; } diff --git a/src/share/vm/code/nmethod.hpp b/src/share/vm/code/nmethod.hpp index 7e7025611f6fe43aaec414173f3e598f47b0ca14..a41c2f448282e9360817d5f91f5aa4cf2601094c 100644 --- a/src/share/vm/code/nmethod.hpp +++ b/src/share/vm/code/nmethod.hpp @@ -69,14 +69,13 @@ class PcDescCache VALUE_OBJ_CLASS_SPEC { friend class VMStructs; private: enum { cache_size = 4 }; - PcDesc* _last_pc_desc; // most recent pc_desc found PcDesc* _pc_descs[cache_size]; // last cache_size pc_descs found public: - PcDescCache() { debug_only(_last_pc_desc = NULL); } + PcDescCache() { debug_only(_pc_descs[0] = NULL); } void reset_to(PcDesc* initial_pc_desc); PcDesc* find_pc_desc(int pc_offset, bool approximate); void add_pc_desc(PcDesc* pc_desc); - PcDesc* last_pc_desc() { return _last_pc_desc; } + PcDesc* last_pc_desc() { return _pc_descs[0]; } }; @@ -178,7 +177,7 @@ class nmethod : public CodeBlob { unsigned int _has_method_handle_invokes:1; // Has this method MethodHandle invokes? // Protected by Patching_lock - unsigned char _state; // {alive, not_entrant, zombie, unloaded) + unsigned char _state; // {alive, not_entrant, zombie, unloaded} #ifdef ASSERT bool _oops_are_stale; // indicates that it's no longer safe to access oops section