On Thu, Dec 20, 2012 at 03:53:44AM -0500, Jean-Philippe Ouellet wrote:
> Hello,
>
> I'm trying to learn about writing high performance servers, and I have a
> few questions not clearly answered by any documentation I can find. I'm
> comfortable with select(), poll(), and kqueue(), but that only goes so
> far. I'm currently looking into how to send static files (over a
> network) with the least amount of overhead.
>
> There was a post [1] on misc@ asking about the status of a sendfile()
> call, but nobody replied (and it seems that splice(2) and tee(2) are
> just GNUisms). It appears that there's been some work on socket splicing
> (see sosplice() in [2]), but there's still no sendfile (or if it's
> there, I must not be looking in the right place [3]).
I do not know of any effort to introduce sendfile(2).
>
> If I want to serve a bunch of files often, is it fine to rely on the
> kernel's filesystem caching? or should I mmap() them into my address
> space and madvise() them to not be swapped out? Is it reasonable to
> stat() the file each time it is served (from my cached copy) to compare
> the file's modification time to the time it was cached? Would this
> actually hit the disk each time? or does the kernel keep that cached?
Filesystem caching should be fine, a lot of effort went into this
lately. File metadata is cached by the kernel vfs layer.
-Otto
>
> It seems obvious to me that it should be be cached, but I can't actually
> find the relevant code. I spent a while digging through the kernel, but
> I don't really know where to look, and I'm not sure I'd recognize what
> I'm looking for if I found it anyway. The closest thing I found to
> something I think might be relevant was some cryptic vfs stuff. :( I'm
> no kernel dev, I don't pretend to understand OpenBSD internals nearly as
> well as I'd like to.
>
> Lastly, What's the OpenBSD community's current opinion on libevent /
> libev. Are they secure / stable enough that they should be considered
> for new code in base? Are they worth using instead of just using
> select/poll/kqueue/event(3) directly?
>
> [1] http://marc.info/?l=openbsd-misc&m=112690025715479&w=2
> [2]
> http://www.openbsd.org/cgi-bin/cvsweb/~checkout~/src/sys/kern/uipc_socket.c
> [3] http://www.openbsd.org/cgi-bin/cvsweb/~checkout~/src/sys/kern/syscalls.c
>
> Many thanks for any and all advice,
> Jean-Philippe Ouellet
