Re: [ck] 2.6.16-ck9

[Juho Saarikko <juhos@mbnet.fi>]

On Wed, 2006-05-03 at 01:01, Con Kolivas wrote:
> On Wednesday 03 May 2006 06:57, Juho Saarikko wrote:
> > I tried to run SetiAtHome at IDLEPRIO, but it competes equally with a
> > while(1); loop run at nice 19. I'm starting to wonder if there isn't
> > some kind of bug in the kernel which results in a program returning from
> > a system call with an in-kernel semaphore held. After all, according to
> > top, SetiAtHome consumes over 90% CPU, and the system consumes only
> > about 1%, so it can't be making system calls all the time either. Or
> > maybe there's some case where the calculations can become confused and
> > think that a semaphore is still being held when it's not.
> >
> > Is there any way to test this ?
> >
> > Anyway, I ran strace on FahCore (a program, launched by SetiAtHome main
> > program, that actually consumes the CPU), and got this:
> >
> >
> > rt_sigprocmask(SIG_BLOCK, [CHLD], [RTMIN], 8) = 0
> > rt_sigaction(SIGCHLD, NULL, {SIG_DFL}, 8) = 0
> > rt_sigprocmask(SIG_SETMASK, [RTMIN], NULL, 8) = 0
> > nanosleep({5, 0}, {5, 0})               = 0
> > nanosleep({0, 0}, NULL)                 = 0
> >
> >
> > This pattern just keeps on repeating, endlessly. Occasionally it also
> > has
> >
> > kill(5432, SIG_0)                       = 0
> >
> > attached to it. 5432 is the parent process, the FAH502-Linux.exe.
> >
> > There is something very strange going on here...
> 
> Find all the threads running with this command:
> ps -wweALo spid,user,priority,ni,pcpu,vsize,time,args

My version of ps doesn't seem to support spid, but by dropping it I got
the thread pids anyway.

> The spid will show you any threads with different pids to the main task. Then 
> check the actual scheduling policy they run at. Perhaps FahCore actually 
> manually sets them to SCHED_NORMAL.

And so it does. Annoying. Time to hack kernel to add a new scheduling
policy, SCHED_STAYIDLE, which is like SCHED_IDLE but cannot be unset
except by root.

Can't make it the default, since a program running at SCHED_IDLE in a
machine with 100% CPU usage by some other program will never process
SIGKILL, and thus can only be killed by setting its scheduling policy to
normal...

Darn obnoxious program, SetiAtHome...

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