Pls review 7023931 (S)
Daniel D. Daugherty
daniel.daugherty at oracle.com
Fri Mar 11 12:37:36 PST 2011
On 3/11/2011 1:14 PM, Paul Hohensee wrote:
> 7023931: PcDescCache::find_pc_desc should not write _last_pc_desc
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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