[Xen-devel] [PATCH 3/5] xen: events: Clean up round-robin evtchn scan.

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

From: Keir Fraser <keir.fraser@xxxxxxxxxx>

Also fixes a couple of boundary cases.

Signed-off-by: Keir Fraser <keir.fraser@xxxxxxxxxx>
Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
[ijc: forward ported from linux-2.6.18-xen.hg 988:c88a02a22a05]
---
 drivers/xen/events.c |   44 ++++++++++++++++++++------------------------
 1 files changed, 20 insertions(+), 24 deletions(-)

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 1fc3192..c49cb6d 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -1026,8 +1026,8 @@ irqreturn_t xen_debug_interrupt(int irq, void *dev_id)
 }
 
 static DEFINE_PER_CPU(unsigned, xed_nesting_count);
-static DEFINE_PER_CPU(unsigned int, last_word_idx) = { BITS_PER_LONG - 1 };
-static DEFINE_PER_CPU(unsigned int, last_bit_idx) = { BITS_PER_LONG - 1 };
+static DEFINE_PER_CPU(unsigned int, current_word_idx);
+static DEFINE_PER_CPU(unsigned int, current_bit_idx);
 
 /*
  * Mask out the i least significant bits of w
@@ -1065,23 +1065,21 @@ static void __xen_evtchn_do_upcall(void)
 #endif
                pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0);
 
-               word_idx = __this_cpu_read(last_word_idx);
-               bit_idx = __this_cpu_read(last_bit_idx);
+               word_idx = __this_cpu_read(current_word_idx);
+               bit_idx = __this_cpu_read(current_bit_idx);
 
                while (pending_words != 0) {
                        unsigned long pending_bits;
                        unsigned long words;
 
-                       word_idx = (word_idx + 1) % BITS_PER_LONG;
                        words = MASK_LSBS(pending_words, word_idx);
 
                        /*
-                        * If we masked out all events, wrap around to the
-                        * beginning.
+                        * If we masked out all events, wrap to beginning.
                         */
                        if (words == 0) {
-                               word_idx = BITS_PER_LONG - 1;
-                               bit_idx = BITS_PER_LONG - 1;
+                               word_idx = 0;
+                               bit_idx = 0;
                                continue;
                        }
                        word_idx = __ffs(words);
@@ -1093,14 +1091,11 @@ static void __xen_evtchn_do_upcall(void)
 
                                pending_bits = active_evtchns(cpu, s, word_idx);
 
-                               bit_idx = (bit_idx + 1) % BITS_PER_LONG;
                                bits = MASK_LSBS(pending_bits, bit_idx);
 
                                /* If we masked out all events, move on. */
-                               if (bits == 0) {
-                                       bit_idx = BITS_PER_LONG - 1;
+                               if (bits == 0)
                                        break;
-                               }
 
                                bit_idx = __ffs(bits);
 
@@ -1117,22 +1112,23 @@ static void __xen_evtchn_do_upcall(void)
                                                generic_handle_irq_desc(irq, 
desc);
                                }
 
-                               /*
-                                * If this is the final port processed, we'll
-                                * pick up here+1 next time.
-                                */
-                               __this_cpu_write(last_word_idx, word_idx);
-                               __this_cpu_write(last_bit_idx, bit_idx);
-                       } while (bit_idx != BITS_PER_LONG - 1);
+                               bit_idx = (bit_idx + 1) % BITS_PER_LONG;
+
+                               /* Next caller starts at last processed + 1 */
+                               __this_cpu_write(current_word_idx,
+                                                bit_idx ? word_idx :
+                                                (word_idx+1) % BITS_PER_LONG);
+                               __this_cpu_write(current_bit_idx, bit_idx);
+                       } while (bit_idx != 0);
 
                        pending_bits = active_evtchns(cpu, s, word_idx);
 
-                       /*
-                        * We handled all ports, so we can clear the
-                        * selector bit.
-                        */
+                       /* If we handled all ports, clear the selector bit. */
                        if (pending_bits == 0)
                                pending_words &= ~(1UL << word_idx);
+
+                       word_idx = (word_idx + 1) % BITS_PER_LONG;
+                       bit_idx = 0;
                }
 
                BUG_ON(!irqs_disabled());
-- 
1.5.6.5


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