code review 58260043: net/http: use a struct instead of a string in transport...

net/http: use a struct instead of a string in transport conn cache key

The Transport's idle connection cache is keyed by a string,
for pre-Go 1.0 reasons.  Ever since Go has been able to use
structs as map keys, there's been a TODO in the code to use
structs instead of allocating strings. This change does that.

Saves 3 allocatins and ~100 bytes of garbage per client
request. But because string hashing is so fast these days
(thanks, Keith), the performance is a wash: what we gain
on GC and not allocating, we lose in slower hashing. (hashing
structs of strings is slower than 1 string)

This seems a bit faster usually, but I've also seen it be a
bit slower. But at least it's how I've wanted it now, and it
the allocation improvements are consistent.

[bradfitz, 2014-01-29 12:52:42]

Hello adg (cc: golang-codereviews@googlegroups.com),

I'd like you to review this change to
https://go.googlecode.com/hg/

[adg, 2014-01-30 07:01:57]

LGMT

[adg, 2014-01-30 08:55:32]

LGTM

[bradfitz, 2014-01-30 08:57:07]

*** Submitted as https://code.google.com/p/go/source/detail?r=22fe13ae3884 ***

net/http: use a struct instead of a string in transport conn cache key

The Transport's idle connection cache is keyed by a string,
for pre-Go 1.0 reasons.  Ever since Go has been able to use
structs as map keys, there's been a TODO in the code to use
structs instead of allocating strings. This change does that.

Saves 3 allocatins and ~100 bytes of garbage per client
request. But because string hashing is so fast these days
(thanks, Keith), the performance is a wash: what we gain
on GC and not allocating, we lose in slower hashing. (hashing
structs of strings is slower than 1 string)

This seems a bit faster usually, but I've also seen it be a
bit slower. But at least it's how I've wanted it now, and it
the allocation improvements are consistent.

LGTM=adg
R=adg
CC=golang-codereviews
https://codereview.appspot.com/58260043

[dvyukov, 2014-01-30 11:27:26]

FYI

---------- Forwarded message ----------
Date: Thu, Jan 30, 2014 at 3:10 PM
Subject: Perf changes on windows-amd64 by net/http: use a struct instead of a
string in transport conn cache key


Change 22fe13ae3884 caused perf changes on windows-amd64:

net/http: use a struct instead of a string in transport conn cache key

The Transport's idle connection cache is keyed by a string,
for pre-Go 1.0 reasons.  Ever since Go has been able to use
structs as map keys, there's been a TODO in the code to use
structs instead of allocating strings. This change does that.

Saves 3 allocatins and ~100 bytes of garbage per client
request. But because string hashing is so fast these days
(thanks, Keith), the performance is a wash: what we gain
on GC and not

http://code.google.com/p/go/source/detail?r=22fe13ae3884

http-1                    old          new      delta
allocs                     57           54      -5.26

http-8                    old          new      delta
allocs                     72           68      -5.56

http://goperfd.appspot.com/perfdetail?commit=22fe13ae3884ef4349cfb78ad5804ebc...