xen: events: Make round-robin scan fairer by snapshotting each l2 word once only
(except for starting l2 word, which we scan in two parts).
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
[ijc: forward ported from linux-2.6.18-xen.hg 990:427276ac595d]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index c49cb6d..0c3f17b 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -1045,7 +1045,9 @@
*/
static void __xen_evtchn_do_upcall(void)
{
+ int start_word_idx, start_bit_idx;
int word_idx, bit_idx;
+ int i;
int cpu = get_cpu();
struct shared_info *s = HYPERVISOR_shared_info;
struct vcpu_info *vcpu_info = __this_cpu_read(xen_vcpu);
@@ -1065,10 +1067,12 @@
#endif
pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0);
- word_idx = __this_cpu_read(current_word_idx);
- bit_idx = __this_cpu_read(current_bit_idx);
+ start_word_idx = __this_cpu_read(current_word_idx);
+ start_bit_idx = __this_cpu_read(current_bit_idx);
- while (pending_words != 0) {
+ word_idx = start_word_idx;
+
+ for (i = 0; pending_words != 0; i++) {
unsigned long pending_bits;
unsigned long words;
@@ -1084,13 +1088,23 @@
}
word_idx = __ffs(words);
+ pending_bits = active_evtchns(cpu, s, word_idx);
+ bit_idx = 0; /* usually scan entire word from start */
+ if (word_idx == start_word_idx) {
+ /* We scan the starting word in two parts */
+ if (i == 0)
+ /* 1st time: start in the middle */
+ bit_idx = start_bit_idx;
+ else
+ /* 2nd time: mask bits done already */
+ bit_idx &= (1UL << start_bit_idx) - 1;
+ }
+
do {
unsigned long bits;
int port, irq;
struct irq_desc *desc;
- pending_bits = active_evtchns(cpu, s, word_idx);
-
bits = MASK_LSBS(pending_bits, bit_idx);
/* If we masked out all events, move on. */
@@ -1121,10 +1135,8 @@
__this_cpu_write(current_bit_idx, bit_idx);
} while (bit_idx != 0);
- pending_bits = active_evtchns(cpu, s, word_idx);
-
- /* If we handled all ports, clear the selector bit. */
- if (pending_bits == 0)
+ /* Scan start_l1i twice; all others once. */
+ if ((word_idx != start_word_idx) || (i != 0))
pending_words &= ~(1UL << word_idx);
word_idx = (word_idx + 1) % BITS_PER_LONG;
