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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>
This commit is contained in:
Keir Fraser 2011-03-03 11:06:28 +00:00 committed by Konrad Rzeszutek Wilk
parent ada6814c87
commit 24b51c2f2d
1 changed files with 21 additions and 9 deletions
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30
drivers/xen/events.c
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@ -1045,7 +1045,9 @@ static DEFINE_PER_CPU(unsigned int, current_bit_idx);
*/
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 @@ static void __xen_evtchn_do_upcall(void)
#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 @@ static void __xen_evtchn_do_upcall(void)
}
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 @@ static void __xen_evtchn_do_upcall(void)
__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;