From edc2d17086a6d21039f45506459cf1b9f40eb95c Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Wed, 15 Aug 2018 16:19:21 -0400 Subject: [PATCH] runtime: remove GODEBUG=gctrace=2 mode It turns out if you set GODEBUG=gctrace=2, it enables an obscure debugging mode that, in addition to printing gctrace statistics, also does a second STW GC following each regular GC. This debugging mode has long since lost its value (you could maybe use it to analyze floating garbage, except that we don't print the gctrace line on the second GC), and it interferes substantially with the operation of the GC by messing up the statistics used to schedule GCs. It's also a source of mark termination GC work when we're in concurrent GC mode, so it's going to interfere with eliminating mark 2. And it's going to get in the way of unifying STW and concurrent GC. This CL removes this debugging mode. Updates #26903. This is preparation for eliminating mark 2 and unifying STW GC and concurrent GC. Change-Id: Ib5bce05d8c4d5b6559c89a65165d49532165df07 Reviewed-on: https://go-review.googlesource.com/c/134316 Run-TryBot: Austin Clements TryBot-Result: Gobot Gobot Reviewed-by: Rick Hudson --- src/runtime/extern.go | 3 +-- src/runtime/mgc.go | 17 ----------------- 2 files changed, 1 insertion(+), 19 deletions(-) diff --git a/src/runtime/extern.go b/src/runtime/extern.go index 1773c8fe7e..3be1eca09c 100644 --- a/src/runtime/extern.go +++ b/src/runtime/extern.go @@ -61,8 +61,7 @@ It is a comma-separated list of name=val pairs setting these named variables: gctrace: setting gctrace=1 causes the garbage collector to emit a single line to standard error at each collection, summarizing the amount of memory collected and the - length of the pause. Setting gctrace=2 emits the same summary but also - repeats each collection. The format of this line is subject to change. + length of the pause. The format of this line is subject to change. Currently, it is: gc # @#s #%: #+#+# ms clock, #+#/#/#+# ms cpu, #->#-># MB, # MB goal, # P where the fields are as follows: diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go index c95b5ed37f..f975011191 100644 --- a/src/runtime/mgc.go +++ b/src/runtime/mgc.go @@ -1558,23 +1558,6 @@ func gcMarkTermination(nextTriggerRatio float64) { // marking is complete so we can turn the write barrier off setGCPhase(_GCoff) gcSweep(work.mode) - - if debug.gctrace > 1 { - startTime = nanotime() - // The g stacks have been scanned so - // they have gcscanvalid==true and gcworkdone==true. - // Reset these so that all stacks will be rescanned. - gcResetMarkState() - finishsweep_m() - - // Still in STW but gcphase is _GCoff, reset to _GCmarktermination - // At this point all objects will be found during the gcMark which - // does a complete STW mark and object scan. - setGCPhase(_GCmarktermination) - gcMark(startTime) - setGCPhase(_GCoff) // marking is done, turn off wb. - gcSweep(work.mode) - } }) _g_.m.traceback = 0 -- 2.50.0