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net/netcheck: improve the preferred DERP hysteresis

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Users in Amsterdam (as one example) were flipping back and forth
between equidistant London & Frankfurt relays too much.

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick 2021-01-11 11:38:49 -08:00 committed by Brad Fitzpatrick
parent 024671406b
commit 676b5b7946
2 changed files with 42 additions and 6 deletions
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30
net/netcheck/netcheck.go
View File

@ -1102,6 +1102,10 @@ func (c *Client) addReportHistoryAndSetPreferredDERP(r *Report) {
c.mu.Lock()
defer c.mu.Unlock()
var prevDERP int
if c.last != nil {
prevDERP = c.last.PreferredDERP
}
if c.prev == nil {
c.prev = map[time.Time]*Report{}
}
@ -1119,9 +1123,9 @@ func (c *Client) addReportHistoryAndSetPreferredDERP(r *Report) {
delete(c.prev, t)
continue
}
for hp, d := range pr.RegionLatency {
if bd, ok := bestRecent[hp]; !ok || d < bd {
bestRecent[hp] = d
for regionID, d := range pr.RegionLatency {
if bd, ok := bestRecent[regionID]; !ok || d < bd {
bestRecent[regionID] = d
}
}
}
@ -1129,13 +1133,27 @@ func (c *Client) addReportHistoryAndSetPreferredDERP(r *Report) {
// Then, pick which currently-alive DERP server from the
// current report has the best latency over the past maxAge.
var bestAny time.Duration
for hp := range r.RegionLatency {
best := bestRecent[hp]
var oldRegionCurLatency time.Duration
for regionID, d := range r.RegionLatency {
if regionID == prevDERP {
oldRegionCurLatency = d
}
best := bestRecent[regionID]
if r.PreferredDERP == 0 || best < bestAny {
bestAny = best
r.PreferredDERP = hp
r.PreferredDERP = regionID
}
}
// If we're changing our preferred DERP but the old one's still
// accessible and the new one's not much better, just stick with
// where we are.
if prevDERP != 0 &&
r.PreferredDERP != prevDERP &&
oldRegionCurLatency != 0 &&
bestAny > oldRegionCurLatency/3*2 {
r.PreferredDERP = prevDERP
}
}
func updateLatency(m map[int]time.Duration, regionID int, d time.Duration) {

18
net/netcheck/netcheck_test.go
View File

@ -195,6 +195,24 @@ type step struct {
wantPrevLen: 1, // t=[0123]s all gone. (too old, older than 10 min)
wantDERP: 3, // only option
},
{
name: "preferred_derp_hysteresis_no_switch",
steps: []step{
{0 * time.Second, report("d1", 4, "d2", 5)},
{1 * time.Second, report("d1", 4, "d2", 3)},
},
wantPrevLen: 2,
wantDERP: 1, // 2 didn't get fast enough
},
{
name: "preferred_derp_hysteresis_do_switch",
steps: []step{
{0 * time.Second, report("d1", 4, "d2", 5)},
{1 * time.Second, report("d1", 4, "d2", 1)},
},
wantPrevLen: 2,
wantDERP: 2, // 2 got fast enough
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {