From b21d677ee9efe431a4acc653a8cfb12650e44cec Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Tue, 8 May 2012 16:51:57 +0200 Subject: stream: fix ratelimiting corner case This fixes inability to make progress in streaming if the quota is set to less than the amount of data that an I/O operation has to write. In this case, limit->dispatched + n will always be above the quota and, due to the "goto retry" to recheck cancellation and allocation, streaming will livelock. This can be reproduced with "block_job_set_speed ide0-hd0 1b". Of course, with this patch the requested limit will not be obeyed. That could be done with another patch that caps is_allocated's n argument by the slice quota. Signed-off-by: Paolo Bonzini Signed-off-by: Kevin Wolf --- block/stream.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) (limited to 'block/stream.c') diff --git a/block/stream.c b/block/stream.c index 25f98e493c..a2c8f67711 100644 --- a/block/stream.c +++ b/block/stream.c @@ -33,19 +33,19 @@ typedef struct { static int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n) { - int64_t delay_ns = 0; int64_t now = qemu_get_clock_ns(rt_clock); if (limit->next_slice_time < now) { limit->next_slice_time = now + SLICE_TIME; limit->dispatched = 0; } - if (limit->dispatched + n > limit->slice_quota) { - delay_ns = limit->next_slice_time - now; - } else { + if (limit->dispatched == 0 || limit->dispatched + n <= limit->slice_quota) { limit->dispatched += n; + return 0; + } else { + limit->dispatched = n; + return limit->next_slice_time - now; } - return delay_ns; } static void ratelimit_set_speed(RateLimit *limit, uint64_t speed) -- cgit v1.2.1