Re: [RFC] extending splice for copy offloading

[Ric Wheeler <rwheeler@redhat.com>]

On 09/26/2013 03:53 PM, Miklos Szeredi wrote:
> On Thu, Sep 26, 2013 at 9:06 PM, Zach Brown <zab@redhat.com> wrote:
>
>>> But I'm not sure it's worth the effort; 99% of the use of this
>>> interface will be copying whole files.  And for that perhaps we need a
>>> different API, one which has been discussed some time ago:
>>> asynchronous copyfile() returns immediately with a pollable event
>>> descriptor indicating copy progress, and some way to cancel the copy.
>>> And that can internally rely on ->direct_splice(), with appropriate
>>> algorithms for determine the optimal  chunk size.
>> And perhaps we don't.  Perhaps we can provide this much simpler
>> data-plane interface that works well enough for most everyone and can
>> avoid going down the async rat hole, yet again.
> I think either buffering or async is needed to get good perforrmace
> without too much complexity in the app (which is not good).  Buffering
> works quite well for regular I/O, so maybe its the way to go here as
> well.
>
> Thanks,
> Miklos
>

Buffering  misses the whole point of the copy offload - the idea is *not* to 
read or write the actual data in the most interesting cases which offload the 
operation to a smart target device or file system.

Regards,

Ric