Factor out a Histogram class from HistogramTimer, and use it to measure external fragmentation

Factor out a Histogram class from HistogramTimer, and use it to measure external fragmentation

BUG=none
TEST=none

Committed: https://code.google.com/p/v8/source/detail?r=12081

[jochen (gone - plz use gerrit), 2012-07-02 11:33:37]

plz review

In contrast to counters, histograms are automatically uploaded to UMA

[Michael Starzinger, 2012-07-02 21:09:56]

Just a few nits. Some of them not even on code that you touched, sorry for that.
:)

Also, I think it's time for a second-order macro of all spaces present in the V8
heap. Yang suggested a similar thing in response to the previous CL introducing
the counters. But you don't need to do that as part of this CL, I can do that
after we landed this one.

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.cc
File src/counters.cc (right):

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.cc#newcode1
src/counters.cc:1: // Copyright 2007-2008 the V8 project authors. All rights
reserved.
2012

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.cc#newcode68
src/counters.cc:68: if (Enabled())
Curly brackets if not on one line.

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.h
File src/counters.h (right):

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.h#newcode1
src/counters.h:1: // Copyright 2007-2008 the V8 project authors. All rights
reserved.
2012

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.h#newcode173
src/counters.h:173: return ptr_;
Aww, that should be on one line.

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.h#newcode202
src/counters.h:202: // Similar to StatsCounter, the class Histogram represents a
dynamically
Can we remove the reference to StatsCounter here? Just "A Histogram represents
[...]"

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.h#newcode220
src/counters.h:220: // Returns false if table is full.
Let's turn that into just one line: "Returns true if this histogram is enabled."

https://chromiumcodereview.appspot.com/10695056/diff/1/src/heap.cc
File src/heap.cc (right):

https://chromiumcodereview.appspot.com/10695056/diff/1/src/heap.cc#newcode449
src/heap.cc:449: static_cast<int>(new_space()->Available()) / 1024);
Better use the "KB" macro here. And on the following lines.

https://chromiumcodereview.appspot.com/10695056/diff/1/src/v8-counters.cc
File src/v8-counters.cc (right):

https://chromiumcodereview.appspot.com/10695056/diff/1/src/v8-counters.cc#new...
src/v8-counters.cc:1: // Copyright 2007-2008 the V8 project authors. All rights
reserved.
2012

https://chromiumcodereview.appspot.com/10695056/diff/1/src/v8-counters.h
File src/v8-counters.h (right):

https://chromiumcodereview.appspot.com/10695056/diff/1/src/v8-counters.h#newc...
src/v8-counters.h:1: // Copyright 2011 the V8 project authors. All rights
reserved.
2012

[jochen (gone - plz use gerrit), 2012-07-13 09:48:07]

I changed the CL to not turn the counters into histogram, but add histograms for
external fragmentation of each space

PTAL

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.cc
File src/counters.cc (right):

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.cc#newcode1
src/counters.cc:1: // Copyright 2007-2008 the V8 project authors. All rights
reserved.
On 2012/07/02 21:09:56, Michael Starzinger wrote:
> 2012

Done.

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.cc#newcode68
src/counters.cc:68: if (Enabled())
On 2012/07/02 21:09:56, Michael Starzinger wrote:
> Curly brackets if not on one line.

Done.

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.h
File src/counters.h (right):

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.h#newcode1
src/counters.h:1: // Copyright 2007-2008 the V8 project authors. All rights
reserved.
On 2012/07/02 21:09:56, Michael Starzinger wrote:
> 2012

Done.

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.h#newcode173
src/counters.h:173: return ptr_;
On 2012/07/02 21:09:56, Michael Starzinger wrote:
> Aww, that should be on one line.

Done.

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.h#newcode202
src/counters.h:202: // Similar to StatsCounter, the class Histogram represents a
dynamically
On 2012/07/02 21:09:56, Michael Starzinger wrote:
> Can we remove the reference to StatsCounter here? Just "A Histogram represents
> [...]"

Done.

https://chromiumcodereview.appspot.com/10695056/diff/1/src/counters.h#newcode220
src/counters.h:220: // Returns false if table is full.
On 2012/07/02 21:09:56, Michael Starzinger wrote:
> Let's turn that into just one line: "Returns true if this histogram is
enabled."

Done.

https://chromiumcodereview.appspot.com/10695056/diff/1/src/v8-counters.h
File src/v8-counters.h (right):

https://chromiumcodereview.appspot.com/10695056/diff/1/src/v8-counters.h#newc...
src/v8-counters.h:1: // Copyright 2011 the V8 project authors. All rights
reserved.
On 2012/07/02 21:09:56, Michael Starzinger wrote:
> 2012

Done.

[Michael Starzinger, 2012-07-13 11:36:38]

LGTM.

As discussed offline, the histogram for the "empty script" (i.e. starting V8,
doing one GC and tearing it down again) shows high fragmentation, because each
space basically just contains the first page. But the instances running no JS at
all should be aggregated away.