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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 <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Paolo Bonzini 2012-05-08 16:51:57 +02:00 committed by Kevin Wolf
parent c6db23958b
commit b21d677ee9
1 changed files with 5 additions and 5 deletions
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10
block/stream.c
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@ -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)