[Qemu-devel] [PATCH 10/15] Revert "openpic: Accelerate pending irq search"

[Scott Wood]

This reverts commit a9bd83f4c65de0058659ede009fa1a241f379edd.

This counting approach is not robust against setting a bit that
was already set, or clearing a bit that was already clear.  Perhaps
that is considered a bug, but besides the lack of any documentation
for that restriction, it's a pretty unpleasant way for the problem
to manifest itself.

It could be made more robust by testing the current value of the
bit before changing the count, but a later patch speeds up IRQ_check
in all cases, not just when there's nothing pending.  Hopefully that
should be adequate to address performance concerns.

Signed-off-by: Scott Wood <address@hidden>
---
 hw/openpic.c |   11 -----------
 1 file changed, 11 deletions(-)

diff --git a/hw/openpic.c b/hw/openpic.c
index e2e7079..cc3e514 100644
--- a/hw/openpic.c
+++ b/hw/openpic.c
@@ -181,7 +181,6 @@ typedef struct IRQ_queue_t {
     uint32_t queue[BF_WIDTH(MAX_IRQ)];
     int next;
     int priority;
-    int pending;    /* nr of pending bits in queue */
 } IRQ_queue_t;
 
 typedef struct IRQ_src_t {
@@ -270,13 +269,11 @@ typedef struct OpenPICState {
 
 static inline void IRQ_setbit(IRQ_queue_t *q, int n_IRQ)
 {
-    q->pending++;
     set_bit(q->queue, n_IRQ);
 }
 
 static inline void IRQ_resetbit(IRQ_queue_t *q, int n_IRQ)
 {
-    q->pending--;
     reset_bit(q->queue, n_IRQ);
 }
 
@@ -292,12 +289,6 @@ static void IRQ_check(OpenPICState *opp, IRQ_queue_t *q)
 
     next = -1;
     priority = -1;
-
-    if (!q->pending) {
-        /* IRQ bitmap is empty */
-        goto out;
-    }
-
     for (i = 0; i < opp->max_irq; i++) {
         if (IRQ_testbit(q, i)) {
             DPRINTF("IRQ_check: irq %d set ivpr_pr=%d pr=%d\n",
@@ -308,8 +299,6 @@ static void IRQ_check(OpenPICState *opp, IRQ_queue_t *q)
             }
         }
     }
-
-out:
     q->next = next;
     q->priority = priority;
 }
-- 
1.7.9.5