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runtime: steal timers from running P's

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Previously we did not steal timers from running P's, because that P
should be responsible for running its own timers. However, if the P
is running a CPU-bound G, this can cause measurable delays in running
ready timers. Also, in CL 214185 we avoided taking the timer lock of a P
with no ready timers, which reduces the chances of timer lock contention.

So, if we can't find any ready timers on sleeping P's, try stealing
them from running P's.

Fixes #38860

Change-Id: I0bf1d5dc56258838bdacccbf89493524e23d7fed
Reviewed-on: https://go-review.googlesource.com/c/go/+/232199
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
This commit is contained in:
Ian Lance Taylor 2020-05-04 16:19:16 -07:00
parent 9bbe899576
commit 9b90491e4a
1 changed files with 8 additions and 5 deletions
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13
src/runtime/proc.go
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@ -2231,11 +2231,14 @@ top:
// Consider stealing timers from p2. // Consider stealing timers from p2.
// This call to checkTimers is the only place where // This call to checkTimers is the only place where
// we hold a lock on a different P's timers. // we hold a lock on a different P's timers.
// Lock contention can be a problem here, so avoid // Lock contention can be a problem here, so
// grabbing the lock if p2 is running and not marked // initially avoid grabbing the lock if p2 is running
// for preemption. If p2 is running and not being // and is not marked for preemption. If p2 is running
// preempted we assume it will handle its own timers. // and not being preempted we assume it will handle its
if i > 2 && shouldStealTimers(p2) { // own timers.
// If we're still looking for work after checking all
// the P's, then go ahead and steal from an active P.
if i > 2 || (i > 1 && shouldStealTimers(p2)) {
tnow, w, ran := checkTimers(p2, now) tnow, w, ran := checkTimers(p2, now)
now = tnow now = tnow
if w != 0 && (pollUntil == 0 || w < pollUntil) { if w != 0 && (pollUntil == 0 || w < pollUntil) {