| commit | ce502b063cd810aa5897e6ce72d545591e9368a0 | [log] [tgz] |
|---|---|---|
| author | Austin Clements <austin@google.com> | Wed Apr 22 17:44:36 2015 -0400 |
| committer | Austin Clements <austin@google.com> | Fri Apr 24 15:13:01 2015 +0000 |
| tree | 989b90d0d2cad15e585ad8f9d9ed94480ff08ff9 | |
| parent | 4e32718d3e478278d0f7e3d6910d563c35f40be0 [diff] |
runtime: use park/ready to wake up GC at end of concurrent mark Currently, the main GC goroutine sleeps on a note during concurrent mark and the first background mark worker or assist to finish marking use wakes up that note to let the main goroutine proceed into mark termination. Unfortunately, the latency of this wakeup can be quite high, since the GC goroutine will typically have lost its P while in the futex sleep, meaning it will be placed on the global run queue and will wait there until some P is kind enough to pick it up. This delay gives the mutator more time to allocate and create floating garbage, growing the heap unnecessarily. Worse, it's likely that background marking has stopped at this point (unless GOMAXPROCS>4), so anything that's allocated and published to the heap during this window will have to be scanned during mark termination while the world is stopped. This change replaces the note sleep/wakeup with a gopark/ready scheme. This keeps the wakeup inside the Go scheduler and lets the garbage collector take advantage of the new scheduler semantics that run the ready()d goroutine immediately when the ready()ing goroutine sleeps. For the json benchmark from x/benchmarks with GOMAXPROCS=4, this reduces the delay in waking up the GC goroutine and entering mark termination once concurrent marking is done from ~100ms to typically <100µs. Change-Id: Ib11f8b581b8914f2d68e0094f121e49bac3bb384 Reviewed-on: https://go-review.googlesource.com/9291 Reviewed-by: Rick Hudson <rlh@golang.org> Reviewed-by: Russ Cox <rsc@golang.org>
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