code review 143160046: syscall: another attempt to keep windows syscall pointe...

syscall: another attempt to keep windows syscall pointers live

This approach was suggested in
https://codereview.appspot.com/138250043/#msg15.
Unlike current version of mksyscall_windows.go,
new code could be used in go.sys and other external
repos without help from asm.

[brainman, 2014-10-03 02:10:33]

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

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

[iant, 2014-10-03 17:58:22]

LGTM

https://codereview.appspot.com/143160046/diff/40001/src/syscall/mksyscall_win...
File src/syscall/mksyscall_windows.go (right):

https://codereview.appspot.com/143160046/diff/40001/src/syscall/mksyscall_win...
src/syscall/mksyscall_windows.go:533: a := make([]string, 0)
For this kind of code I always just write
    var a []string
Why call make when you're going to build using append anyhow?

[r, 2014-10-03 18:05:56]

https://codereview.appspot.com/143160046/diff/40001/src/syscall/mksyscall_win...
File src/syscall/mksyscall_windows.go (right):

https://codereview.appspot.com/143160046/diff/40001/src/syscall/mksyscall_win...
src/syscall/mksyscall_windows.go:533: a := make([]string, 0)
On 2014/10/03 17:58:22, iant wrote:
> For this kind of code I always just write
>     var a []string
> Why call make when you're going to build using append anyhow?

i'd use

make([]string, 0, len(f.Params))

which is more efficient.

[brainman, 2014-10-05 02:15:24]

*** Submitted as https://code.google.com/p/go/source/detail?r=be3fe3a11200 ***

syscall: another attempt to keep windows syscall pointers live

This approach was suggested in
https://codereview.appspot.com/138250043/#msg15.
Unlike current version of mksyscall_windows.go,
new code could be used in go.sys and other external
repos without help from asm.

LGTM=iant
R=golang-codereviews, iant, r
CC=golang-codereviews
https://codereview.appspot.com/143160046

https://codereview.appspot.com/143160046/diff/40001/src/syscall/mksyscall_win...
File src/syscall/mksyscall_windows.go (right):

https://codereview.appspot.com/143160046/diff/40001/src/syscall/mksyscall_win...
src/syscall/mksyscall_windows.go:533: a := make([]string, 0)
On 2014/10/03 18:05:56, r wrote:
> On 2014/10/03 17:58:22, iant wrote:
> > For this kind of code I always just write
> >     var a []string
> > Why call make when you're going to build using append anyhow?
> 
> i'd use
> 
> make([]string, 0, len(f.Params))
> 
> which is more efficient. 

Done.

[gobot, 2014-10-05 02:39:48]

This changed caused perf changes on linux-amd64-perf:


http-1                    old          new      delta
sys-stack              393216       327680     -16.67

http-2                    old          new      delta
sys-stack              491520       458752      -6.67

http-4                    old          new      delta
sys-stack              819200       720896     -12.00

http://build.golang.org/perfdetail?commit=be3fe3a1120009c4d0b9b5d497b0c8d2741...



—gobot

[brainman, 2014-10-05 04:12:49]

On 2014/10/05 02:39:48, gobot wrote:
> This changed caused perf changes on linux-amd64-perf:
> 
> 
> http-1                    old          new      delta
> sys-stack              393216       327680     -16.67
> 
> http-2                    old          new      delta
> sys-stack              491520       458752      -6.67
> 
> http-4                    old          new      delta
> sys-stack              819200       720896     -12.00
> 
>
http://build.golang.org/perfdetail?commit=be3fe3a1120009c4d0b9b5d497b0c8d2741...
> 
> 
> 
> —gobot

I don't see how these large changes are possible.

Alex