From ffd5687a8217e6829d2248dd0698f18c0e128ac2 Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Wed, 19 Jul 2017 14:18:08 -0400 Subject: runtime: only trace mark assists that do work Currently we trace mark assists even if they're satisfied entirely by stealing. This means even if background marking is keeping up with allocation, we'll still emit a trace event every N bytes of allocation. The event will be a few microseconds, if that, but they're frequent enough that, when zoomed out in the trace view, it looks like all of the time is spent in mark assists even if almost none is. Change this so we only emit a trace event if the assist actually has to do assisting. This makes the traces of these events far more useful. Change-Id: If4aed1c413b814341ef2fba61d2f10751d00451b Reviewed-on: https://go-review.googlesource.com/50030 Run-TryBot: Austin Clements Reviewed-by: Rick Hudson --- src/runtime/mgcmark.go | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go index dbca5cd1c7..9029d19d43 100644 --- a/src/runtime/mgcmark.go +++ b/src/runtime/mgcmark.go @@ -415,10 +415,7 @@ func gcAssistAlloc(gp *g) { return } - if trace.enabled { - traceGCMarkAssistStart() - } - + traced := false retry: // Compute the amount of scan work we need to do to make the // balance positive. When the required amount of work is low, @@ -454,13 +451,18 @@ retry: if scanWork == 0 { // We were able to steal all of the credit we // needed. - if trace.enabled { + if traced { traceGCMarkAssistDone() } return } } + if trace.enabled && !traced { + traced = true + traceGCMarkAssistStart() + } + // Perform assist work systemstack(func() { gcAssistAlloc1(gp, scanWork) @@ -503,7 +505,7 @@ retry: // At this point either background GC has satisfied // this G's assist debt, or the GC cycle is over. } - if trace.enabled { + if traced { traceGCMarkAssistDone() } } -- cgit v1.2.3-54-g00ecf