From 635f8049a713dcef23723f6e5575bb5b34894b5c Mon Sep 17 00:00:00 2001 From: Simon Marlow Date: Mon, 15 Feb 2010 09:32:05 +0000 Subject: [PATCH] fix lost context switches in GHCi (fixes test 3429(ghci)) --- rts/Schedule.c | 30 +++++++++++++----------------- 1 file changed, 13 insertions(+), 17 deletions(-) diff --git a/rts/Schedule.c b/rts/Schedule.c index c61bbc7..66af8be 100644 --- a/rts/Schedule.c +++ b/rts/Schedule.c @@ -1188,36 +1188,32 @@ scheduleHandleStackOverflow (Capability *cap, Task *task, StgTSO *t) static rtsBool scheduleHandleYield( Capability *cap, StgTSO *t, nat prev_what_next ) { - // Reset the context switch flag. We don't do this just before - // running the thread, because that would mean we would lose ticks - // during GC, which can lead to unfair scheduling (a thread hogs - // the CPU because the tick always arrives during GC). This way - // penalises threads that do a lot of allocation, but that seems - // better than the alternative. - cap->context_switch = 0; - /* put the thread back on the run queue. Then, if we're ready to * GC, check whether this is the last task to stop. If so, wake * up the GC thread. getThread will block during a GC until the * GC is finished. */ -#ifdef DEBUG - if (t->what_next != prev_what_next) { - debugTrace(DEBUG_sched, - "--<< thread %ld (%s) stopped to switch evaluators", - (long)t->id, what_next_strs[t->what_next]); - } -#endif - + ASSERT(t->_link == END_TSO_QUEUE); // Shortcut if we're just switching evaluators: don't bother // doing stack squeezing (which can be expensive), just run the // thread. - if (t->what_next != prev_what_next) { + if (cap->context_switch == 0 && t->what_next != prev_what_next) { + debugTrace(DEBUG_sched, + "--<< thread %ld (%s) stopped to switch evaluators", + (long)t->id, what_next_strs[t->what_next]); return rtsTrue; } + // Reset the context switch flag. We don't do this just before + // running the thread, because that would mean we would lose ticks + // during GC, which can lead to unfair scheduling (a thread hogs + // the CPU because the tick always arrives during GC). This way + // penalises threads that do a lot of allocation, but that seems + // better than the alternative. + cap->context_switch = 0; + IF_DEBUG(sanity, //debugBelch("&& Doing sanity check on yielding TSO %ld.", t->id); checkTSO(t)); -- 1.7.10.4