Re: ksoftirqd? (Was: Re: [PATCH] Preemption Latency Measurement Tool)

[Andrea Arcangeli <andrea@suse.de>]

On Sat, Sep 22, 2001 at 10:51:16PM +0200, Roger Larsson wrote:
> On Saturday 22 September 2001 15.14, Andrea Arcangeli wrote:
> > On Sat, Sep 22, 2001 at 02:56:58PM +0200, Roger Larsson wrote:
> > > Hi,
> > >
> > > We have a new kid on the block since we started thinking of a preemptive
> > > kernel.
> > >
> > > ksoftirqd...
> > >
> > > Running with nice 19 (shouldn't it really be -19?)
> 
> I repeat this question - should it be nice 19 and not nice -19 (not nice)?

Being it +19 it is light with respect to the other tasks in the system,
mainly considering there's one for each cpu.

> Sep 22 22:37:38 jeloin logger: *** ./stress_dbench begin ***
> Sep 22 22:37:42 jeloin kernel: ksoftirqd: do_softirq
> Sep 22 22:37:44 jeloin last message repeated 2 times
> Sep 22 22:37:48 jeloin kernel: Latency   8ms PID     7 %% kupdated
> Sep 22 22:37:49 jeloin kernel: ksoftirqd: do_softirq
> Sep 22 22:38:19 jeloin last message repeated 18 times
> Sep 22 22:38:20 jeloin su: (to root) roger on /dev/pts/2
> Sep 22 22:38:20 jeloin PAM-unix2[988]: session started for user root, service 
> su
> Sep 22 22:38:23 jeloin kernel: ksoftirqd: do_softirq
> Sep 22 22:38:24 jeloin modprobe: modprobe: Can't locate module net-pf-10
> Sep 22 22:38:24 jeloin kernel: ksoftirqd: do_softirq
> Sep 22 22:38:58 jeloin last message repeated 20 times
> Sep 22 22:39:05 jeloin last message repeated 4 times
> Sep 22 22:42:03 jeloin kernel: ksoftirqd: do_softirq
> Sep 22 22:43:58 jeloin logger: *** ./stress_dbench end ***

one reschedule every few seconds sounds ok.

> Possibly but the other case is quite common too...

if you try to put a printk also in do_softirq you'll see why it is
not the common case :)

also you may want to put the printk in the schedule() path, ksoftirqd
may just be rescheduled once, and run many of the do_softirq().

Andrea