Pls review 7023931 (S)
paul.hohensee at oracle.com
Fri Mar 11 12:51:22 PST 2011
Thanks, Dan, for the quick review. Yes, I meant to change it to ".".
kinda wierd to be a ":" there.
On 3/11/11 3:37 PM, Daniel D. Daugherty wrote:
> On 3/11/2011 1:14 PM, Paul Hohensee wrote:
>> 7023931: PcDescCache::find_pc_desc should not write _last_pc_desc
> Thumbs up.
> No comments.
> No code comments.
> line 329 (new): Did you mean to change that ':' to '.'
>> The nmethod PcDescCache cached the last looked-up descriptor in a shared
>> field called _last_pc_desc. This is fine in a single-threaded
>> but in a multi-threaded, multi-socket enviroment, frequent writes cause
>> "block bouncing". I.e., the cache line containing _last_pc_desc is
>> being moved among the caches on different sockets. This process hurts
>> stack walking performance, especially on multi-socket Intel systems.
>> The fix is to eliminate _last_pc_desc and use _pcdescs instead.
>> The latter
>> is written only once when it's added to the cache, avoiding the block
>> bouncing issue. Use of _pcdescs instead of _last_pc_desc means that
>> there are slightly few "hits", but that doesn't seem to affect
>> Tested using SPECjvm2008's serial sub-benchmark and full nsks.
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