lkml.org 
[lkml]   [2001]   [Apr]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH for 2.5] preemptible kernel
Date
In message <OF37B0793C.6B15F182-ON88256A27.0007C3EF@LocalDomain> you write:
> > Priority inversion is not handled in Linux kernel ATM BTW, there
> > are already situations where a realtime task can cause a deadlock
> > with some lower priority system thread (I believe there is at least
> > one case of this known with realtime ntpd on 2.4)
>
> I see your point here, but need to think about it. One question:
> isn't it the case that the alternative to using synchronize_kernel()
> is to protect the read side with explicit locks, which will themselves
> suppress preemption? If so, why not just suppress preemption on the read
> side in preemptible kernels, and thus gain the simpler implementation
> of synchronize_kernel()? You are not losing any preemption latency
> compared to a kernel that uses traditional locks, in fact, you should
> improve latency a bit since the lock operations are more expensive than
> are simple increments and decrements. As usual, what am I missing
> here? ;-)

Already preempted tasks.

> Another approach would be to define a "really low" priority that noone
> other than synchronize_kernel() was allowed to use. Then the UP
> implementation of synchronize_kernel() could drop its priority to
> this level, yield the CPU, and know that all preempted tasks must
> have obtained and voluntarily yielded the CPU before synchronize_kernel()
> gets it back again.

Or "never", because I'm running RC5 etc. 8(.

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

\
 
 \ /
  Last update: 2005-03-22 13:24    [W:0.029 / U:2.772 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site