lkml.org 
[lkml]   [2002]   [Jan]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [2.4.17/18pre] VM and swap - it's really unusable
Date
On January 8, 2002 10:17 pm, Robert Love wrote:
> On Tue, 2002-01-08 at 15:59, Daniel Phillips wrote:
>
> > And while I'm enumerating differences, the preemptable kernel (in this
> > incarnation) has a slight per-spinlock cost, while the non-preemptable kernel
> > has the fixed cost of checking for rescheduling, at intervals throughout all
> > 'interesting' kernel code, essentially all long-running loops. But by clever
> > coding it's possible to finesse away almost all the overhead of those loop
> > checks, so in the end, the non-preemptible low-latency patch has a slight
> > efficiency advantage here, with emphasis on 'slight'.
>
> True (re spinlock weight in preemptible kernel) but how is that not
> comparable to explicit scheduling points? Worse, the preempt-kernel
> typically does its preemption on a branch on return to interrupt
> (similar to user space's preemption). What better time to check and
> reschedule if needed?

The per-spinlock cost I was refering to is the cost of the inc/dec per
spinlock. I guess this cost is small enough as to be hard to measure, but
I have not tried so I don't know. Curiously, none of the people I've heard
making pronouncements on the overhead of your preempt patch seem to have
measured it either.

--
Daniel
-
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 13:15    [W:0.270 / U:4.080 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site