From 3ef0296a0b77d70585e23be93a5144e764a2781e Mon Sep 17 00:00:00 2001 From: David Vrabel Date: Thu, 15 Aug 2013 13:21:05 +0100 Subject: xen/events: document behaviour when scanning the start word for events The original comment on the scanning of the start word on the 2nd pass did not reflect the actual behaviour (the code was incorrectly masking bit_idx instead of the pending word itself). The documented behaviour is not actually required since if event were pending in the MSBs, they would be immediately scanned anyway as we go through the loop again. Update the documentation to reflect this (instead of trying to change the behaviour). Signed-off-by: David Vrabel Signed-off-by: Konrad Rzeszutek Wilk Reviewed-by: Boris Ostrovsky --- drivers/xen/events.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) (limited to 'drivers/xen') diff --git a/drivers/xen/events.c b/drivers/xen/events.c index c8b9d9fc77b5..0b14a9bbbb0a 100644 --- a/drivers/xen/events.c +++ b/drivers/xen/events.c @@ -1388,14 +1388,21 @@ static void __xen_evtchn_do_upcall(void) pending_bits = active_evtchns(cpu, s, word_idx); bit_idx = 0; /* usually scan entire word from start */ + /* + * We scan the starting word in two parts. + * + * 1st time: start in the middle, scanning the + * upper bits. + * + * 2nd time: scan the whole word (not just the + * parts skipped in the first pass) -- if an + * event in the previously scanned bits is + * pending again it would just be scanned on + * the next loop anyway. + */ 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 { -- cgit v1.2.3