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Commit ab7f863e authored by Scott Rixner's avatar Scott Rixner Committed by Konrad Rzeszutek Wilk
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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: default avatarIan 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: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent 71eef7d1

drivers/xen/events.c

+65 −7
Original line number Diff line number Diff line
@@ -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;



			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];

			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);



			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());