Re: [PATCH] Use direct I/O for loop devices

[Jan Beulich <jbeulich@suse.com>]

On 17.08.2022 22:46, Demi Marie Obenour wrote:
> This is a huge performance improvement for two reasons:
> 
> 1. It uses the filesystem’s asynchronous I/O support, rather than using
>    synchronous I/O.
> 2. It bypasses the page cache, removing a redundant layer of caching and
>    associated overhead.
> ---
>  tools/hotplug/Linux/block | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/hotplug/Linux/block b/tools/hotplug/Linux/block
> index 2691b56951c9b82094471a141b9e0bed04abb929..75785f3a5422c4a5f962a4cd4f6acae5080d036d 100644
> --- a/tools/hotplug/Linux/block
> +++ b/tools/hotplug/Linux/block
> @@ -330,7 +330,7 @@ mount it read-write in a guest domain."
>          else
>            roflag=''
>          fi
> -        do_or_die losetup $roflag "$loopdev" "$file"
> +        do_or_die losetup --direct-io=on $roflag "$loopdev" "$file"

I guess you want to first check (maybe in tools/configure) that losetup
actually supports that option. The old-ish one I'm looking at doesn't,
according to its --help output at least.

Jan