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fs/accounting: make edge bandwidth limiters have smaller bursts to make smoother 

This change decreases the edge limiter burst size which dramatically
increases the smoothness of the bandwidth limiting.

The core bandwidth limiter remains with a large burst so it isn't
affected by double rate limiting on the edge limiters.

See: #4395
See: https://forum.rclone.org/t/bwlimit-is-not-really-smooth/20947
This commit is contained in:
Nick Craig-Wood 2020-12-14 21:02:20 +00:00
parent 0a932dc1f2
commit 463a18aa07
1 changed files with 30 additions and 14 deletions
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44
fs/accounting/token_bucket.go
View File

@ -27,6 +27,16 @@ const (
type buckets [TokenBucketSlots]*rate.Limiter
// can't request more than this many bytes at once
//
// set small for edge bandwidth limiters, but big for core bandwidth
// limiters since we may be using both at once
var maxBurstSizes = [TokenBucketSlots]int{
TokenBucketSlotAccounting: 4 * 1024 * 1024,
TokenBucketSlotTransportRx: 4 * 1024,
TokenBucketSlotTransportTx: 4 * 1024,
}
// tokenBucket holds info about the rate limiters in use
type tokenBucket struct {
mu sync.RWMutex // protects the token bucket variables
@ -53,28 +63,26 @@ func (bs *buckets) _setOff() {
}
}
const maxBurstSize = 4 * 1024 * 1024 // must be bigger than the biggest request
// make a new empty token bucket with the bandwidth(s) given
func newTokenBucket(bandwidth fs.BwPair) (tbs buckets) {
bandwidthAccounting := fs.SizeSuffix(-1)
if bandwidth.Tx > 0 {
tbs[TokenBucketSlotTransportTx] = rate.NewLimiter(rate.Limit(bandwidth.Tx), maxBurstSize)
tbs[TokenBucketSlotTransportTx] = rate.NewLimiter(rate.Limit(bandwidth.Tx), maxBurstSizes[TokenBucketSlotTransportTx])
bandwidthAccounting = bandwidth.Tx
}
if bandwidth.Rx > 0 {
tbs[TokenBucketSlotTransportRx] = rate.NewLimiter(rate.Limit(bandwidth.Rx), maxBurstSize)
tbs[TokenBucketSlotTransportRx] = rate.NewLimiter(rate.Limit(bandwidth.Rx), maxBurstSizes[TokenBucketSlotTransportRx])
if bandwidth.Rx > bandwidthAccounting {
bandwidthAccounting = bandwidth.Rx
}
}
if bandwidthAccounting > 0 {
tbs[TokenBucketSlotAccounting] = rate.NewLimiter(rate.Limit(bandwidthAccounting), maxBurstSize)
tbs[TokenBucketSlotAccounting] = rate.NewLimiter(rate.Limit(bandwidthAccounting), maxBurstSizes[TokenBucketSlotAccounting])
}
for _, tb := range tbs {
for i, tb := range tbs {
if tb != nil {
// empty the bucket
err := tb.WaitN(context.Background(), maxBurstSize)
err := tb.WaitN(context.Background(), maxBurstSizes[i])
if err != nil {
fs.Errorf(nil, "Failed to empty token bucket: %v", err)
}
@ -149,20 +157,28 @@ func (tb *tokenBucket) StartTokenTicker(ctx context.Context) {
}()
}
// LimitBandwidth sleeps for the correct amount of time for the passage
// of n bytes according to the current bandwidth limit
// LimitBandwidth sleeps for the correct amount of time for the
// passage of n bytes according to the current bandwidth limit.
func (tb *tokenBucket) LimitBandwidth(i TokenBucketSlot, n int) {
tb.mu.RLock()
t := tb.curr[i]
maxBurstSize := maxBurstSizes[i]
tb.mu.RUnlock()
// Limit the transfer speed if required
if tb.curr[i] != nil {
err := tb.curr[i].WaitN(context.Background(), n)
if err != nil {
fs.Errorf(nil, "Token bucket error: %v", err)
if t != nil && n > 0 {
// wait in chunks of maxBurstSize
for toWait := maxBurstSize; n > 0; n -= toWait {
if n < maxBurstSize {
toWait = n
}
err := t.WaitN(context.Background(), toWait)
if err != nil {
fs.Errorf(nil, "Token bucket error: %v", err)
}
}
}
tb.mu.RUnlock()
}
// SetBwLimit sets the current bandwidth limit