[Libguestfs] [PATCH libnbd 1/3] golang: examples: Do not initialize pread buffer

[Richard W.M. Jones]

On Sun, Mar 06, 2022 at 10:27:28PM +0200, Nir Soffer wrote:
> The aio_copy example checks errors properly, so it will not leak
> uninitialized memory to the destination image. Testing shows 5% speedup
> when copying a real image.
> 
> $ qemu-nbd --read-only --persistent --shared 8 --cache none --aio native \
>     --socket /tmp/src.sock --format raw fedora-35-data.raw &
> 
> $ hyperfine -p "sleep 5" "./aio_copy-init $SRC >/dev/null" "./aio_copy-no-init $SRC >/dev/null"
> 
> Benchmark 1: ./aio_copy-init nbd+unix:///?socket=/tmp/src.sock >/dev/null
>   Time (mean ± σ):      1.452 s ±  0.027 s    [User: 0.330 s, System: 0.489 s]
>   Range (min … max):    1.426 s …  1.506 s    10 runs
> 
> Benchmark 2: ./aio_copy-no-init nbd+unix:///?socket=/tmp/src.sock >/dev/null
>   Time (mean ± σ):      1.378 s ±  0.009 s    [User: 0.202 s, System: 0.484 s]
>   Range (min … max):    1.369 s …  1.399 s    10 runs
> 
> Summary
>   './aio_copy-no-init nbd+unix:///?socket=/tmp/src.sock >/dev/null' ran
>     1.05 ± 0.02 times faster than './aio_copy-init nbd+unix:///?socket=/tmp/src.sock >/dev/null'
> 
> Signed-off-by: Nir Soffer <nsoffer at redhat.com>
> ---
>  golang/examples/aio_copy/aio_copy.go       | 5 +++++
>  golang/examples/simple_copy/simple_copy.go | 5 +++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/golang/examples/aio_copy/aio_copy.go b/golang/examples/aio_copy/aio_copy.go
> index bb20b478..89eac4df 100644
> --- a/golang/examples/aio_copy/aio_copy.go
> +++ b/golang/examples/aio_copy/aio_copy.go
> @@ -84,20 +84,25 @@ func main() {
>  	err = h.ConnectUri(flag.Arg(0))
>  	if err != nil {
>  		panic(err)
>  	}
>  
>  	size, err := h.GetSize()
>  	if err != nil {
>  		panic(err)
>  	}
>  
> +	err = h.SetPreadInitialize(false)
> +	if err != nil {
> +		panic(err)
> +	}
> +

In patch #2 you added a comment above the call.

Because this is an example and so people may just copy the code
blindly without understanding it, I think adding a comment here and
below is worth doing too.

> diff --git a/golang/examples/simple_copy/simple_copy.go b/golang/examples/simple_copy/simple_copy.go
> index e8fa1f76..2a2ed0ff 100644
> --- a/golang/examples/simple_copy/simple_copy.go
> +++ b/golang/examples/simple_copy/simple_copy.go
> @@ -63,20 +63,25 @@ func main() {
>  	err = h.ConnectUri(flag.Arg(0))
>  	if err != nil {
>  		panic(err)
>  	}
>  
>  	size, err := h.GetSize()
>  	if err != nil {
>  		panic(err)
>  	}
>  
> +	err = h.SetPreadInitialize(false)
> +	if err != nil {
> +		panic(err)
> +	}
> +

And above this one.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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