It is possible for rate limited writes to keep overshooting a slice's
quota by a tiny amount causing the slice-aligned waiting period to
effectively halve the rate.
Signed-off-by: Wolfgang Bumiller <w.bumil...@proxmox.com>
---
Copied the Ccs from the discussion thread, hope that's fine, as I also
just noticed that for my reply containing this snippet I had hit reply
on the mail that did not contain those Ccs yet, sorry about that.
include/qemu/ratelimit.h | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/include/qemu/ratelimit.h b/include/qemu/ratelimit.h
index 8dece483f5..1b38291823 100644
--- a/include/qemu/ratelimit.h
+++ b/include/qemu/ratelimit.h
@@ -36,7 +36,7 @@ typedef struct {
static inline int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
{
int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
- uint64_t delay_slices;
+ double delay_slices;
assert(limit->slice_quota && limit->slice_ns);
@@ -55,12 +55,11 @@ static inline int64_t ratelimit_calculate_delay(RateLimit
*limit, uint64_t n)
return 0;
}
- /* Quota exceeded. Calculate the next time slice we may start
- * sending data again. */
- delay_slices = (limit->dispatched + limit->slice_quota - 1) /
- limit->slice_quota;
+ /* Quota exceeded. Wait based on the excess amount and then start a new
+ * slice. */
+ delay_slices = (double)limit->dispatched / limit->slice_quota;
limit->slice_end_time = limit->slice_start_time +
- delay_slices * limit->slice_ns;
+ (uint64_t)(delay_slices * limit->slice_ns);
return limit->slice_end_time - now;
}
--
2.11.0
