unexpected idprio 31 behavior on 9.2-BETA2 and 9.2-RC1

[John Baldwin]

On Monday, July 07, 2014 4:39:02 am Harald Schmalzbauer wrote:
> Bezüglich John Baldwin's Nachricht vom 04.09.2013 15:58 (localtime):
> > On Thursday, August 08, 2013 10:41:12 am Eric van Gyzen wrote:
> >> On 08/08/2013 09:19, Eric van Gyzen wrote:
> >>> On 08/06/2013 14:23, J David wrote:
> >>>> On Tue, Aug 6, 2013 at 1:59 PM, Eric van Gyzen <eric at vangyzen.net> 
wrote:
> >>>>>> on an otherwise idle amd64 system with 4 CPUs.  The first command in 
> > the
> >>>>>> build.log file:
> >>>>>>
> >>>>>>     rm -rf /usr/obj/home/freebsd/tmp
> >>>>>>
> >>>>>> took over three minutes.  It should have taken about three /seconds/.
> >>>>>>
> >>>>>> "uptime" reported a load average of around 1.00.
> >>>>>> "top" showed no threads (user or kernel) using CPU.
> >>>>>> "iostat" showed an average of less than 20 tps on ada0.
> >>>>>> "rm" was usually in the RUN state.
> >>>> We are looking at something similar.  Would you be able to try to
> >>>> reproduce it using a kernel with:
> >>>>
> >>>> nooptions	SCHED_ULE
> >>>> options		SCHED_4BSD
> >>>>
> >>>> to see if it makes a difference?  It seems to, but the problem is
> >>>> inconsistent enough that I can't be sure.
> >>> The 4BSD scheduler does //not// exhibit this problem.  I tested with the
> >>> latest releng/9.2 (r254054) and an otherwise GENERIC config.
> >>
> >> To be thorough, I built a GENERIC kernel at the same rev, and it still
> >> exhibits the problem.
> > 
> > Please try this change:
> > 
> > Index: sched_ule.c
> > ===================================================================
> > --- sched_ule.c	(revision 255020)
> > +++ sched_ule.c	(working copy)
> > @@ -243,7 +243,7 @@ struct tdq {
> >  	int		tdq_transferable;	/* Transferable thread count. */
> >  	short		tdq_switchcnt;		/* Switches this tick. */
> >  	short		tdq_oldswitchcnt;	/* Switches last tick. */
> > -	u_char		tdq_lowpri;		/* Lowest priority thread. */
> > +	u_short		tdq_lowpri;		/* Lowest priority thread. */
> >  	u_char		tdq_ipipending;		/* IPI pending. */
> >  	u_char		tdq_idx;		/* Current insert index. */
> >  	u_char		tdq_ridx;		/* Current removal index. */
> > @@ -2323,7 +2323,7 @@ sched_choose(void)
> >  		tdq->tdq_lowpri = td->td_priority;
> >  		return (td);
> >  	}
> > -	tdq->tdq_lowpri = PRI_MAX_IDLE;
> > +	tdq->tdq_lowpri = PRI_MAX_IDLE + 1;
> >  	return (PCPU_GET(idlethread));
> >  }
> 
> Hello,
> 
> the fix above still applies cleanly to 9.3-RC3.
> Was ist solved differently? Or just slipped through?

No one ever told me that they tested it and that it worked.  If it works I 
will happily commit it, but it is too late for 9.3.

-- 
John Baldwin