Skip to content
Permalink
Browse files

xen: events: Process event channels notifications in round-robin order.

Avoids fairness issue resulting from domain 0 processing lowest
numbered event channel first.

Fixes bug #1115 "Event channel port scanning unfair".

Bugzilla: http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1115
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
[ijc: forward ported from linux-2.6.18-xen.hg 324:7fe1c6d02a2b
 various variables have different names in this tree:
  l1  -> pending_words
  l2  -> pending_bits
  l1i -> word_idx
  l2i -> bit_idx]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
  • Loading branch information...
rixner authored and konradwilk committed Mar 3, 2011
1 parent 71eef7d commit ab7f863e4183057dc494f3180199934a9637d401
Showing with 65 additions and 7 deletions.
  1. +65 −7 drivers/xen/events.c
@@ -1027,6 +1027,11 @@ irqreturn_t xen_debug_interrupt(int irq, void *dev_id)

static DEFINE_PER_CPU(unsigned, xed_nesting_count);

/*
* Mask out the i least significant bits of w
*/
#define MASK_LSBS(w, i) (w & ((~0UL) << i))

/*
* Search the CPUs pending events bitmasks. For each one found, map
* the event number to an irq, and feed it into do_IRQ() for
@@ -1038,6 +1043,9 @@ static DEFINE_PER_CPU(unsigned, xed_nesting_count);
*/
static void __xen_evtchn_do_upcall(void)
{
static unsigned int last_word_idx = BITS_PER_LONG - 1;
static unsigned int last_bit_idx = BITS_PER_LONG - 1;
int word_idx, bit_idx;
int cpu = get_cpu();
struct shared_info *s = HYPERVISOR_shared_info;
struct vcpu_info *vcpu_info = __this_cpu_read(xen_vcpu);
@@ -1056,17 +1064,50 @@ static void __xen_evtchn_do_upcall(void)
wmb();
#endif
pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0);

word_idx = last_word_idx;
bit_idx = last_bit_idx;

while (pending_words != 0) {
unsigned long pending_bits;
int word_idx = __ffs(pending_words);
pending_words &= ~(1UL << word_idx);
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 (words == 0) {
word_idx = BITS_PER_LONG - 1;
bit_idx = BITS_PER_LONG - 1;
continue;
}
word_idx = __ffs(words);

while ((pending_bits = active_evtchns(cpu, s, word_idx)) != 0) {
int bit_idx = __ffs(pending_bits);
int port = (word_idx * BITS_PER_LONG) + bit_idx;
int irq = evtchn_to_irq[port];
do {
unsigned long bits;
int port, irq;
struct irq_desc *desc;

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;
break;
}

bit_idx = __ffs(bits);

/* Process port. */
port = (word_idx * BITS_PER_LONG) + bit_idx;
irq = evtchn_to_irq[port];

mask_evtchn(port);
clear_evtchn(port);

@@ -1075,7 +1116,24 @@ static void __xen_evtchn_do_upcall(void)
if (desc)
generic_handle_irq_desc(irq, desc);
}
}

/*
* If this is the final port processed, we'll
* pick up here+1 next time.
*/
last_word_idx = word_idx;
last_bit_idx = bit_idx;

} while (bit_idx != BITS_PER_LONG - 1);

pending_bits = active_evtchns(cpu, s, word_idx);

/*
* We handled all ports, so we can clear the
* selector bit.
*/
if (pending_bits == 0)
pending_words &= ~(1UL << word_idx);
}

BUG_ON(!irqs_disabled());

0 comments on commit ab7f863

Please sign in to comment.
You can’t perform that action at this time.