Re: [ANN] Userspace M-on-N threading model implementation. Alpharelease.

[Bill Davidsen]

Jakub Jelinek wrote:
> On Sun, Feb 04, 2007 at 03:12:32PM -0500, Bill Davidsen wrote:
>   
> > Arjan van de Ven wrote:
> >     
> > > > Because user threading can avoid context switches, there will always be 
> > > > cases where it will outperform o/s threads for hardware reasons.
> > > >         
> > > actually.. switching from one "real" thread to another in Linux is not
> > > an actual context switch in the hardware sense... at least this part of
> > > your argument seems to be incorrect ;)
> > >
> > >       
> > How does that work? Switching between kernel threads requires going into 
> > the kernel, user level thread switches are all done in user mode.
> >
> > Do you have some way to change o/s threads w/o going into the kernel?
> >     
>
> But going into kernel is not very expensive on Linux.
>
> On the other side, the overhead you need to add for every single syscall
> that might block for the M:N threads and the associated complications
> which make it far harder to conform to POSIX IMHO far outweight the costs
> of going into the kernel for a context switch.

That really wasn't my question, Arjan said that switching real threads 
wasn't a context switch in the hardware sense, and I was asking if I 
missed something. It may be cheap, but it would seem to be a context 
switch none-the-less.

--
bill davidsen <davidsen@xxxxxxx>
 CTO TMR Associates, Inc
 Doing interesting things with small computers since 1979

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/