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os: (*File).Write should not allocate #9370

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jeffallen opened this issue Dec 17, 2014 · 5 comments
Closed

os: (*File).Write should not allocate #9370

jeffallen opened this issue Dec 17, 2014 · 5 comments
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@jeffallen
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On tip (go version devel +6262902) the following test program shows that os.(*File).Write makes 2 allocations. http://play.golang.org/p/6tjQO4vdlE

(You can't see the problem on playground but you can see it when running locally.)

It would be better if os.(_File).Write did not allocate, as it is a hot path in typical Go servers. For comparison, os.(_File).Read does not allocate.

See also: https://groups.google.com/forum/#!searchin/golang-nuts/Write$20allocates/golang-nuts/0hfeLJP1LSk/u5QfV6cDIsoJ
@ianlancetaylor
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This is issue #8618.

@jeffallen
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Well, last time we talked (in that thread) you agreed that it might be worth patching since os is right at the core of the std library.

This is the fix: https://go-review.googlesource.com/1730

@bradfitz
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This feels different than #8618. This is about the compiler optimizing concrete type == interface value to not create an interface value when the types differ.

@bradfitz bradfitz reopened this Dec 22, 2014
@bradfitz
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/cc @rsc, who wanted this open from https://go-review.googlesource.com/#/c/1730/ "Let's just fix the compiler instead. It can do those comparisons without creating interface values."

@mikioh mikioh changed the title os.(*File).Write should not allocate os: (*File).Write should not allocate Dec 23, 2014
@josharian
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Started on this. WIP (still rough) at https://github.com/josharian/go/compare/9370. Input welcomed.

josharian added a commit to josharian/go that referenced this issue Dec 25, 2014
@josharian
cmd/gc: evaluate concrete == interface without allocating
9bf98db 
Consider an interface value i of type I and concrete value c of type C.

Prior to this CL, i==c was evaluated as
	I(c) == i

As of Go 1.4, all interfaces hold pointers, so evaluating I(c) allocates.

This CL changes the evaluation of i==c to
	x, ok := i.(C); ok && x == c

The new generated code is shorter, uses less stack space,
does not allocate, and makes one runtime call instead of two.

This kind of comparison occurs in 38 places in the stdlib,
mostly in the net and os packages.

benchmark                     old ns/op     new ns/op     delta
BenchmarkCmpIfaceConcrete     31.6          7.92          -74.94%
BenchmarkCmpEfaceConcrete     29.7          7.91          -73.37%

Fixes golang#9370.

Change-Id: I7c4555950bcd6406ee5c613be1f2128da2c9a2b7
josharian added a commit to josharian/go that referenced this issue Dec 25, 2014
@josharian
cmd/gc: evaluate concrete == interface without allocating
c2e508d 
Consider an interface value i of type I and concrete value c of type C.

Prior to this CL, i==c was evaluated as
	I(c) == i

As of Go 1.4, all interfaces hold pointers, so evaluating I(c) allocates.

This CL changes the evaluation of i==c to
	x, ok := i.(C); ok && x == c

The new generated code is shorter, uses less stack space,
does not allocate, and makes one runtime call instead of two.

This kind of comparison occurs in 38 places in the stdlib,
mostly in the net and os packages.

benchmark                     old ns/op     new ns/op     delta
BenchmarkCmpIfaceConcrete     31.6          7.92          -74.94%
BenchmarkCmpEfaceConcrete     29.7          7.91          -73.37%

Fixes golang#9370.

Change-Id: I7c4555950bcd6406ee5c613be1f2128da2c9a2b7
josharian added a commit to josharian/go that referenced this issue Dec 25, 2014
@josharian
cmd/gc: evaluate concrete == interface without allocating
3f5a5cc 
Consider an interface value i of type I and concrete value c of type C.

Prior to this CL, i==c was evaluated as
	I(c) == i

As of Go 1.4, all interfaces hold pointers, so evaluating I(c) allocates.

This CL changes the evaluation of i==c to
	x, ok := i.(C); ok && x == c

The new generated code is shorter, uses less stack space,
does not allocate, and makes one runtime call instead of two.

This kind of comparison occurs in 38 places in the stdlib,
mostly in the net and os packages.

benchmark                     old ns/op     new ns/op     delta
BenchmarkCmpIfaceConcrete     31.6          7.92          -74.94%
BenchmarkCmpEfaceConcrete     29.7          7.91          -73.37%

Fixes golang#9370.

Change-Id: I7c4555950bcd6406ee5c613be1f2128da2c9a2b7
josharian added a commit to josharian/go that referenced this issue Dec 25, 2014
@josharian
cmd/gc: evaluate concrete == interface without allocating
eaabb84 
Consider an interface value i of type I and concrete value c of type C.

Prior to this CL, i==c was evaluated as
	I(c) == i

As of Go 1.4, all interfaces hold pointers, so evaluating I(c) allocates.

This CL changes the evaluation of i==c to
	x, ok := i.(C); ok && x == c

The new generated code is shorter, uses less stack space,
does not allocate, and makes one runtime call instead of two.

This kind of comparison occurs in 38 places in the stdlib,
mostly in the net and os packages.

benchmark                     old ns/op     new ns/op     delta
BenchmarkCmpIfaceConcrete     31.6          7.92          -74.94%
BenchmarkCmpEfaceConcrete     29.7          7.91          -73.37%

Fixes golang#9370.

Change-Id: I7c4555950bcd6406ee5c613be1f2128da2c9a2b7
josharian added a commit to josharian/go that referenced this issue Dec 25, 2014
@josharian
cmd/gc: evaluate concrete == interface without allocating
ea9e660 
Consider an interface value i of type I and concrete value c of type C.

Prior to this CL, i==c was evaluated as
	I(c) == i

Evaluating I(c) can allocate.

This CL changes the evaluation of i==c to
	x, ok := i.(C); ok && x == c

The new generated code is shorter, uses less stack space,
does not allocate, and makes one runtime call instead of two.

This kind of comparison occurs in 38 places in the stdlib,
mostly in the net and os packages.

benchmark                     old ns/op     new ns/op     delta
BenchmarkEqEfaceConcrete      29.5          7.92          -73.15%
BenchmarkEqIfaceConcrete      32.1          7.90          -75.39%
BenchmarkNeEfaceConcrete      29.9          7.90          -73.58%
BenchmarkNeIfaceConcrete      35.9          7.90          -77.99%

Fixes golang#9370.

Change-Id: I7c4555950bcd6406ee5c613be1f2128da2c9a2b7
josharian added a commit to josharian/go that referenced this issue Dec 26, 2014
@josharian
cmd/gc: evaluate concrete == interface without allocating
2b2d1c9 
Consider an interface value i of type I and concrete value c of type C.

Prior to this CL, i==c was evaluated as
	I(c) == i

Evaluating I(c) can allocate.

This CL changes the evaluation of i==c to
	x, ok := i.(C); ok && x == c

The new generated code is shorter and does not allocate directly.

If C is small, as it is in every instance in the stdlib,
the new code also uses less stack space
and makes one runtime call instead of two.

If C is very large, the original implementation is used.
The cutoff for "very large" is 1<<16,
following the stack vs heap cutoff used elsewhere.

This kind of comparison occurs in 38 places in the stdlib,
mostly in the net and os packages.

benchmark                     old ns/op     new ns/op     delta
BenchmarkEqEfaceConcrete      29.5          7.92          -73.15%
BenchmarkEqIfaceConcrete      32.1          7.90          -75.39%
BenchmarkNeEfaceConcrete      29.9          7.90          -73.58%
BenchmarkNeIfaceConcrete      35.9          7.90          -77.99%

Fixes golang#9370.

Change-Id: I7c4555950bcd6406ee5c613be1f2128da2c9a2b7
josharian added a commit to josharian/go that referenced this issue Dec 29, 2014
@josharian
cmd/gc: evaluate concrete == interface without allocating
adfd5e4 
Consider an interface value i of type I and concrete value c of type C.

Prior to this CL, i==c was evaluated as
	I(c) == i

Evaluating I(c) can allocate.

This CL changes the evaluation of i==c to
	x, ok := i.(C); ok && x == c

The new generated code is shorter and does not allocate directly.

If C is small, as it is in every instance in the stdlib,
the new code also uses less stack space
and makes one runtime call instead of two.

If C is very large, the original implementation is used.
The cutoff for "very large" is 1<<16,
following the stack vs heap cutoff used elsewhere.

This kind of comparison occurs in 38 places in the stdlib,
mostly in the net and os packages.

benchmark                     old ns/op     new ns/op     delta
BenchmarkEqEfaceConcrete      29.5          7.92          -73.15%
BenchmarkEqIfaceConcrete      32.1          7.90          -75.39%
BenchmarkNeEfaceConcrete      29.9          7.90          -73.58%
BenchmarkNeIfaceConcrete      35.9          7.90          -77.99%

Fixes golang#9370.

Change-Id: I7c4555950bcd6406ee5c613be1f2128da2c9a2b7
josharian added a commit to josharian/go that referenced this issue Jan 6, 2015
@josharian
cmd/gc: evaluate concrete == interface without allocating
a09bb87 
Consider an interface value i of type I and concrete value c of type C.

Prior to this CL, i==c was evaluated as
	I(c) == i

Evaluating I(c) can allocate.

This CL changes the evaluation of i==c to
	x, ok := i.(C); ok && x == c

The new generated code is shorter and does not allocate directly.

If C is small, as it is in every instance in the stdlib,
the new code also uses less stack space
and makes one runtime call instead of two.

If C is very large, the original implementation is used.
The cutoff for "very large" is 1<<16,
following the stack vs heap cutoff used elsewhere.

This kind of comparison occurs in 38 places in the stdlib,
mostly in the net and os packages.

benchmark                     old ns/op     new ns/op     delta
BenchmarkEqEfaceConcrete      29.5          7.92          -73.15%
BenchmarkEqIfaceConcrete      32.1          7.90          -75.39%
BenchmarkNeEfaceConcrete      29.9          7.90          -73.58%
BenchmarkNeIfaceConcrete      35.9          7.90          -77.99%

Fixes golang#9370.

Change-Id: I7c4555950bcd6406ee5c613be1f2128da2c9a2b7
josharian added a commit to josharian/go that referenced this issue Jan 9, 2015
@josharian
cmd/gc: evaluate concrete == interface without allocating
c64859d 
Consider an interface value i of type I and concrete value c of type C.

Prior to this CL, i==c was evaluated as
	I(c) == i

Evaluating I(c) can allocate.

This CL changes the evaluation of i==c to
	x, ok := i.(C); ok && x == c

The new generated code is shorter and does not allocate directly.

If C is small, as it is in every instance in the stdlib,
the new code also uses less stack space
and makes one runtime call instead of two.

If C is very large, the original implementation is used.
The cutoff for "very large" is 1<<16,
following the stack vs heap cutoff used elsewhere.

This kind of comparison occurs in 38 places in the stdlib,
mostly in the net and os packages.

benchmark                     old ns/op     new ns/op     delta
BenchmarkEqEfaceConcrete      29.5          7.92          -73.15%
BenchmarkEqIfaceConcrete      32.1          7.90          -75.39%
BenchmarkNeEfaceConcrete      29.9          7.90          -73.58%
BenchmarkNeIfaceConcrete      35.9          7.90          -77.99%

Fixes golang#9370.

Change-Id: I7c4555950bcd6406ee5c613be1f2128da2c9a2b7
josharian added a commit to josharian/go that referenced this issue Feb 5, 2015
@josharian
cmd/gc: evaluate concrete == interface without allocating
fc95b48 
Consider an interface value i of type I and concrete value c of type C.

Prior to this CL, i==c was evaluated as
	I(c) == i

Evaluating I(c) can allocate.

This CL changes the evaluation of i==c to
	x, ok := i.(C); ok && x == c

The new generated code is shorter and does not allocate directly.

If C is small, as it is in every instance in the stdlib,
the new code also uses less stack space
and makes one runtime call instead of two.

If C is very large, the original implementation is used.
The cutoff for "very large" is 1<<16,
following the stack vs heap cutoff used elsewhere.

This kind of comparison occurs in 38 places in the stdlib,
mostly in the net and os packages.

benchmark                     old ns/op     new ns/op     delta
BenchmarkEqEfaceConcrete      29.5          7.92          -73.15%
BenchmarkEqIfaceConcrete      32.1          7.90          -75.39%
BenchmarkNeEfaceConcrete      29.9          7.90          -73.58%
BenchmarkNeIfaceConcrete      35.9          7.90          -77.99%

Fixes golang#9370.

Change-Id: I7c4555950bcd6406ee5c613be1f2128da2c9a2b7
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@bradfitz @josharian @jeffallen @ianlancetaylor @gopherbot