| commit bdfc5375f219d6def81effda4e57cb56d01fc917 |
| Author: Sergei Trofimovich <slyfox@gentoo.org> |
| Date: Tue Aug 30 12:10:54 2016 +0100 |
| |
| rts: enable parallel GC scan of large (32M+) allocation area |
| |
| Parallel GC does not scan large allocation area (-A) |
| effectively as it does not do work stealing from nursery |
| by default. |
| |
| That leads to large imbalance when only one of threads |
| overflows allocation area: most of GC threads finish |
| quickly (as there is not much to collect) and sit idle |
| waiting while single GC thread finishes scan of single |
| allocation area for that thread. |
| |
| The patch enables work stealing for (equivalent of -qb0) |
| allocation area of -A32M or higher. |
| |
| Tested on a highlighting-kate package from Trac #9221 |
| |
| On 8-core machine the difference is around 5% faster |
| of wall-clock time. On 24-core VM the speedup is 20%. |
| |
| Signed-off-by: Sergei Trofimovich <siarheit@google.com> |
| |
| Test Plan: measured wall time and GC parallelism on highlighting-kate build |
| |
| Reviewers: austin, bgamari, erikd, simonmar |
| |
| Reviewed By: bgamari, simonmar |
| |
| Subscribers: thomie |
| |
| Differential Revision: https://phabricator.haskell.org/D2483 |
| |
| GHC Trac Issues: #9221 |
| |
| diff --git a/rts/RtsFlags.c b/rts/RtsFlags.c |
| index fda33f0..7a719b9 100644 |
| --- a/rts/RtsFlags.c |
| +++ b/rts/RtsFlags.c |
| @@ -237,1 +237,1 @@ void initRtsFlagsDefaults(void) |
| - RtsFlags.ParFlags.parGcLoadBalancingGen = 1; |
| + RtsFlags.ParFlags.parGcLoadBalancingGen = ~0u; /* auto, based on -A */ |
| @@ -1398,2 +1390,19 @@ static void normaliseRtsOpts (void) |
| } |
| |
| +#ifdef THREADED_RTS |
| + if (RtsFlags.ParFlags.parGcLoadBalancingGen == ~0u) { |
| + StgWord alloc_area_bytes |
| + = RtsFlags.GcFlags.minAllocAreaSize * BLOCK_SIZE; |
| + |
| + // If allocation area is larger that CPU cache |
| + // we can finish scanning quicker doing work-stealing |
| + // scan. Trac #9221 |
| + // 32M looks big enough not to fit into L2 cache |
| + // of popular modern CPUs. |
| + if (alloc_area_bytes >= 32 * 1024 * 1024) { |
| + RtsFlags.ParFlags.parGcLoadBalancingGen = 0; |
| + } else { |
| + RtsFlags.ParFlags.parGcLoadBalancingGen = 1; |
| + } |
| + } |
| +#endif |
