Repeated trace in log file with error

[adrianlzt]

/kind bug

What steps did you take and what happened:
https://play.golang.com/p/6l8KNG_iOsM

Configuring klog to write to a file and logtostderr=false, the log file is openned and wrote three times with the same content.

Removing the flush, writes three times the headers, but no content.

What did you expect to happen:
Only one open and write.

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

[DirectXMan12]

/priority important-soon

[adrianlzt]

https://github.com/kubernetes/klog/blob/master/klog.go#L926

	// Files are created in decreasing severity order, so as soon as we find one
	// has already been created, we can stop.
	for s := sev; s >= infoLog && l.file[s] == nil; s-- {

This is going to create a new file for each severity. Opening three times (error, warning and info) the same file if we have defined a particular log_file.

Not sure why the comment says that it is going to stop.

[DirectXMan12]

it will stop if the files for a particular verbosity already exists (e.g. l.file[s] != nil) -- it just doesn't have a good definition of "already created". We should probably fix this somewhere though.

[tallclair]

It's also configured to write to multiple files:

klog/klog.go

Lines 765 to 777 in e88f730

	switch s {
	case fatalLog:
	l.file[fatalLog].Write(data)
	fallthrough
	case errorLog:
	l.file[errorLog].Write(data)
	fallthrough
	case warningLog:
	l.file[warningLog].Write(data)
	fallthrough
	case infoLog:
	l.file[infoLog].Write(data)
	}

[liggitt]

/reopen

the attempted fix for this caused severe performance regressions

[k8s-ci-robot]

@liggitt: Reopened this issue.

In response to this:

/reopen

the attempted fix for this caused severe performance regressions

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[liggitt]

fix was reverted in #69