Re: [OSS Proxy] [osspd:bugs] #4 alsap output too fast

[Miklos S. <mi...@sz...>]

On Tue, Feb 5, 2013 at 7:53 PM, Anand Avati <av...@re...> wrote:

>
> splice() would give us zero user-to-kernel copy, but still results in memory
> copies, no?

Splice allows userspace to move pages from one kernel subsystem to
another (disk to network, etc...) without the page being ever copied
or mapped.  Unlike mmap it does not allow access to the *contents* of
the page.

If you do need to access the contents from userspace then the pages
need to be mapped to avoid copies.  If no access is needed to the
contents then mapping the pages just adds unnecessary overhead.

Think of splice as an operation that can move pages to or from a page
array (the pipe) in userspace.

Thanks,
Miklos