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Commit 24b51c2f authored by Keir Fraser's avatar Keir Fraser Committed by Konrad Rzeszutek Wilk
Browse files

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: default avatarKeir Fraser <keir.fraser@citrix.com>
Signed-off-by: default avatarIan Campbell <ian.campbell@citrix.com>
[ijc: forward ported from linux-2.6.18-xen.hg 990:427276ac595d]
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent ada6814c

drivers/xen/events.c

+21 −9
Original line number Diff line number Diff line
@@ -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);



		word_idx = start_word_idx;



		while (pending_words != 0) {

		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;