Re: RES: KQueue vs Select (NetMap)

On Thursday 29 May 2014 01:57:38 Fred Pedrisa wrote:
> Hello,
> 
> There are 4 threads, and a total of 32 FDs. What do you think ?

I think it is time for you to try it and find out...

I suspect it wouldn't make much difference at all if you just implement select 
semantics with kqueue.  

> -----Mensagem original-----
> De: owner-freebsd-current_at_freebsd.org
> [mailto:owner-freebsd-current_at_freebsd.org] Em nome de Adrian Chadd
> Enviada em: quinta-feira, 29 de maio de 2014 01:52
> Para: Fred Pedrisa
> Cc: freebsd-current; Jan Bramkamp
> Assunto: Re: KQueue vs Select (NetMap)
> 
> If your netmap thread(s) just have one or two FDs in some low range (say,
> under FD 8 or 10) - no.
> 
> If you have a whole bunch of active FDs and your netmap threads get FDs that
> are high - then yes. select() operates on a bitmap of FD numbers. So if
> your netmap FD is like, FD 8 and it's the highest FD that you're interested
> in, select() only has to scan up to that FD. So it scans up to 8 FDs. If
> you have a very active program and it has thousands of FDs open, select()
> has to check all the FDs in the bitmap to see if they're set before getting
> to your netmap FD.
> 
> So yes. kqueue() is actually rather nice.
> 
> 
> 
> -a
> 
> On 28 May 2014 21:48, Fred Pedrisa <fredhps10_at_hotmail.com> wrote:
> > Hello,
> > 
> > Ok, but in practice, is there any performance gain by moving from select
> 
> to kQueue implementation ? Or is it not significant at all ?
> 
> > -----Mensagem original-----
> > De: adrian.chadd_at_gmail.com [mailto:adrian.chadd_at_gmail.com] Em nome de
> > Adrian Chadd Enviada em: quinta-feira, 29 de maio de 2014 01:46
> > Para: Fred Pedrisa
> > Cc: Jan Bramkamp; freebsd-current
> > Assunto: Re: KQueue vs Select (NetMap)
> > 
> > The advantage is being able to include it in the rest of a kqueue IO loop
> 
> where it's doing other things.
> 
> > -a
> > 
> > On 28 May 2014 20:53, Fred Pedrisa <fredhps10_at_hotmail.com> wrote:
> >> Hello,
> >> 
> >> Yes, but kqueue support was added in recent commits as it says in the
> >> netmap changelog, is there any advantage ?
> >> 
> >> -----Mensagem original-----
> >> De: owner-freebsd-current_at_freebsd.org
> >> [mailto:owner-freebsd-current_at_freebsd.org] Em nome de Jan Bramkamp
> >> Enviada em: quinta-feira, 29 de maio de 2014 00:30
> >> Para: freebsd-current_at_freebsd.org
> >> Assunto: Re: KQueue vs Select (NetMap)
> >> 
> >> On 29.05.2014 03:04, Fred Pedrisa wrote:
> >>> Hey Guys,
> >>> 
> >>> 
> >>> 
> >>> How does kQueue performs over select with netmap ?
> >> 
> >> You are asking for a comparison between apples and oranges. Netmap is
> >> an API for high performance access to the low-level features of
> >> modern NICs. It works on batches of frames in hardware queues.
> >> 
> >> The kqueue() and kevent() system calls are an event notification API.
> >> It is mostly used by application dealing with a large amount of
> >> non-blocking sockets (or other file descriptors). It reduces overhead
> >> inherent in
> >> select() and poll() by preserving state between calls. It also
> >> supports multiple types of events (read ready, write ready, timer
> >> expired, async i/o, etc.).
> >> 
> >> Afaik the netmap pseudo-device supports only select() and poll().
> >> This is no performance problem because every thread will only deal
> >> with a small number of file descriptors to netmap devices.
> >> 
> >> Netmap is designed to bypass the FreeBSD IP stack (for most frames).
> >> Kqueue is designed to scale to many sockets per process within the
> >> FreeBSD IP stack.
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