Re: port-vax/55415: vax no longer preempts in a timely fashion

[Greg Oster <oster%netbsd.org@localhost>]

The following reply was made to PR port-vax/55415; it has been noted by GNATS.

From: Greg Oster <oster%netbsd.org@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: port-vax/55415: vax no longer preempts in a timely fashion
Date: Mon, 6 Jul 2020 08:50:11 -0600

 On 6/26/20 12:55 AM, Anders Magnusson wrote:
 > The following reply was made to PR port-vax/55415; it has been noted by GNATS.
 > 
 > From: Anders Magnusson <ragge%tethuvudet.se@localhost>
 > To: gnats-bugs%netbsd.org@localhost, port-vax-maintainer%netbsd.org@localhost,
 >   gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost, oster%netbsd.org@localhost
 > Cc:
 > Subject: Re: port-vax/55415: vax no longer preempts in a timely fashion
 > Date: Fri, 26 Jun 2020 08:54:15 +0200
 > 
 >   Den 2020-06-25 kl. 17:00, skrev Greg Oster:
 >   > The following reply was made to PR port-vax/55415; it has been noted by GNATS.
 >   >
 >   > From: Greg Oster <oster%netbsd.org@localhost>
 >   > To: gnats-bugs%netbsd.org@localhost
 >   > Cc:
 >   > Subject: Re: port-vax/55415: vax no longer preempts in a timely fashion
 >   > Date: Thu, 25 Jun 2020 08:55:50 -0600
 >   >
 >   >   On 6/25/20 3:15 AM, Anders Magnusson wrote:
 >   >   > The following reply was made to PR port-vax/55415; it has been noted by GNATS.
 >   >   >
 >   >   > From: Anders Magnusson <ragge%tethuvudet.se@localhost>
 >   >   > To: gnats-bugs%netbsd.org@localhost
 >   >   > Cc:
 >   >   > Subject: Re: port-vax/55415: vax no longer preempts in a timely fashion
 >   >   > Date: Thu, 25 Jun 2020 11:10:42 +0200
 >   >   >
 >   >   >   Will it work if you only restore the removed line in cpu.h?
 >   >
 >   >   Yes, yes it does!  So it's just one line that needs to be restored to
 >   >   get things working properly.
 >   >
 >   Great!
 >   
 >   The other missing line should not be needed as I understand the code in
 >   sched_resched_cpu().
 >   ci_want_resched should always be set already when cpu_need_resched() is
 >   called.
 >   
 >   I'll try to fire up my 4000/90 this weekend and see if I can find this bug.
 >   
 >   -- R
 >   
 > 
 I had a few minutes to poke at this again... and can confirm that the 
 issue can be seen using simh as well.  I note that setting 
 ci_want_resched to 4 (RESCHED_UPREEMPT) or 8 (RESCHED_KPREEMPT) is 
 insufficient -- it is only with setting ci_want_resched to 1 (i.e. 
 likely blowing away the currently set value of 4) that scheduling 
 behaves properly.  Also: using:
 
    ci_want_resched |= 1;
 
 is also insufficient -- which tells me it's the lack of '4' or '8' being 
 set that is the thing, not the setting of '1'.  But I havn't been able 
 to figure out why yet...
 
 
 Later...
 
 Greg Oster