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7023931: PcDescCache::find_pc_desc should not write _last_pc_desc

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Remove _last_pc_desc and use pcdescs[0] instead.

Reviewed-by: dcubed, coleenp, ysr
This commit is contained in:
Paul Hohensee 2011-03-11 16:09:55 -05:00
parent 4770417e71
commit f38a80b837
2 changed files with 21 additions and 19 deletions
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33
hotspot/src/share/vm/code/nmethod.cpp
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@ -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;
}