Re: Syslets, Threadlets, generic AIO support, v6

[Eric Dumazet <dada1@cosmosbay.com>]

Linus Torvalds a écrit :
> 
> On Wed, 30 May 2007, Eric Dumazet wrote:
>> So yes, reimplement sendfile() should help to find last splice() bugs, and as
>> a bonus it could add non blocking disk io, (O_NONBLOCK on input file ->
>> socket)
> 
> Well, to get those kinds of advantages, you'd have to use splice directly, 
> since sendfile() hasn't supported nonblocking disk IO, and the interface 
> doesn't really allow for it.

sendfile() interface doesnt allow it, but if you open("somediskfile", O_RDONLY 
| O_NONBLOCK), then splice() based sendfile() can perform a non blocking disk 
io, (while starting an io with readahead)

I actually use this trick myself :)

(splice(disk -> pipe, NONBLOCK), splice(pipe -> worker))

non blocking disk io, + zero copy :)

> 
> In fact, since nonblocking accesses require also some *polling* method, 
> and we don't have that for files, I suspect the best option for those 
> things is to simply mix AIO and splice(). AIO tends to be the right thing 
> for disk waits (read: short, often cached), and if we can improve AIO 
> performance for the cached accesses (which is exactly what the threadlets 
> should hopefully allow us to do), I would seriously suggest going that 
> route.
> 
> But the pure "use splice to _implement_ sendfile()" thing is worth doing 
> for all the other reasons, even if nonblocking file access is not likely 
> one of them.
> 
> 		Linus
> 
>