lkml.org 
[lkml]   [2004]   [May]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: Slab cache reap and CPU availability
Date
> 
> Dimitri Sivanich <sivanich@sgi.com> wrote:
> >
> > Hi all,
> >
> > I have a fairly general question about the slab cache reap code.
> >
> > In running realtime noise tests on the 2.6 kernels (spinning to detect periods
> > of CPU unavailability to RT threads) on an IA/64 Altix system, I have found the
> > cache_reap code to be the source of a number of larger holdoffs (periods of
> > CPU unavailability). These can last into the 100's of usec on 1300 MHz CPUs.
> > Since this code runs periodically every few seconds as a timer softirq on all
> > CPUs, holdoffs can occur frequently.
> >
> > Has anyone looked into less interruptive alternatives to running cache_reap
> > this way (for the 2.6 kernel), or maybe looked into potential optimizations
> > to the routine itself?
> >
>
> Do you have stack backtraces? I thought the problem was via the RCU
> softirq callbacks, not via the timer interrupt. Dipankar spent some time
> looking at the RCU-related problem but solutions are not comfortable.
>
> What workload is triggering this?
>

The IA/64 backtrace with all the cruft removed looks as follows:

0xa000000100149ac0 reap_timer_fnc+0x100
0xa0000001000f4d70 run_timer_softirq+0x2d0
0xa0000001000e9440 __do_softirq+0x200
0xa0000001000e94e0 do_softirq+0x80
0xa000000100017f50 ia64_handle_irq+0x190

The system is running mostly AIM7, but I've seen holdoffs > 30 usec with
virtually no load on the system.

Which uncomfortable solutions (which could relate to this case) have been
investigated?


Dimitri Sivanich <sivanich@sgi.com>
-
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 14:03    [W:0.126 / U:0.056 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site