GNU bug report logs - #11437
nice: tests: please disable on hurd-i386

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Samuel Thibault <samuel.thibault <at> gnu.org>
To: bug-coreutils <at> gnu.org
Subject: coreutils: Please disable misc/nice test on hurd-i386]
Date: Tue, 8 May 2012 20:39:49 +0200

(From http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=670477 )

Hello,

The misc/nice test currently fails on hurd-i386 because the nice support
there is not precise enough: the Mach kernel, which handles scheduling
priorities, has only 32 priority levels, and not 40, so conversion is
used, but that becomes not precise enough for the misc/nice test.  Apart
from that, the nice tool works fine. Could you disable that test on
hurd-i386?

Samuel

Message #8 received at 11437 <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: Samuel Thibault <samuel.thibault <at> gnu.org>
Cc: 11437 <at> debbugs.gnu.org
Subject: Re: bug#11437: coreutils: Please disable misc/nice test on hurd-i386]
Date: Tue, 08 May 2012 12:54:08 -0600

[Message part 1 (text/plain, inline)]

On 05/08/2012 12:39 PM, Samuel Thibault wrote:
> (From http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=670477 )
> 
> Hello,
> 
> The misc/nice test currently fails on hurd-i386 because the nice support
> there is not precise enough: the Mach kernel, which handles scheduling
> priorities, has only 32 priority levels, and not 40, so conversion is
> used, but that becomes not precise enough for the misc/nice test.  Apart
> from that, the nice tool works fine. Could you disable that test on
> hurd-i386?

What is the mapping between the kernel's 32 levels and the
POSIX-mandated minimum of 40 niceness levels (that is, which niceness
levels are rounded to a neighbor)?  Can we rewrite the test to use just
niceness levels provided by Hurd?  Would it be any simpler if Hurd were
to define NZERO as 32, and provide only even niceness values?  In fact,
if you could track 64 niceness levels, and just have every pair of
niceness levels map to the kernel priorities, then you would be
POSIX-compliant (POSIX doesn't require that niceness level 0 and 1 have
any difference in scheduling, only that you can have niceness levels
between 0 and 2*NZERO-1).

In other words, I'm proposing:

NZERO=32

Niceness    Kernel priority
-32         0
-31         0
-30         1
-29         1
...
0           16
1           16
2           17
...
29          30
30          31
31          31

(assuming kernel priority is like niceness, where a lower number is
higher priority)

If you make that fix to Hurd, then the mapping will just work, and
coreutils will start passing the test.

-- 
Eric Blake   eblake <at> redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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Message #11 received at 11437 <at> debbugs.gnu.org (full text, mbox):

From: Samuel Thibault <samuel.thibault <at> gnu.org>
To: Eric Blake <eblake <at> redhat.com>
Cc: bug-hurd <at> gnu.org, 11437 <at> debbugs.gnu.org
Subject: Re: bug#11437: coreutils: Please disable misc/nice test on hurd-i386]
Date: Sat, 12 May 2012 17:18:36 +0200

Eric Blake, le Tue 08 May 2012 12:54:08 -0600, a écrit :
> On 05/08/2012 12:39 PM, Samuel Thibault wrote:
> > The misc/nice test currently fails on hurd-i386 because the nice support
> > there is not precise enough: the Mach kernel, which handles scheduling
> > priorities, has only 32 priority levels, and not 40, so conversion is
> > used, but that becomes not precise enough for the misc/nice test.  Apart
> > from that, the nice tool works fine. Could you disable that test on
> > hurd-i386?
> 
> What is the mapping between the kernel's 32 levels and the
> POSIX-mandated minimum of 40 niceness levels (that is, which niceness
> levels are rounded to a neighbor)?  Can we rewrite the test to use just
> niceness levels provided by Hurd?

It's a simple factor 2:

#define MACH_PRIORITY_TO_NICE(prio) (2 * ((prio) - 12))
#define NICE_TO_MACH_PRIORITY(nice) (12 + ((nice) / 2))

> In fact,
> if you could track 64 niceness levels, and just have every pair of
> niceness levels map to the kernel priorities, then you would be
> POSIX-compliant (POSIX doesn't require that niceness level 0 and 1 have
> any difference in scheduling, only that you can have niceness levels
> between 0 and 2*NZERO-1).

Right, but that'd means that libc has to remember all priorities, to
be able to return them, including other processes (it's not only about
nice, but also get/setpriority).

OTOH, we could as well extend mach's priorities to 40 levels and change
the mappping. The only issue with that is that when using a patched libc
(using >32 priority values) with a non-patched kernel (refusing them),
some nice values will be refused by kernel. Maybe we can consider it's
not a problem that people have to upgrade their kernel to fix it.

Samuel

Message #14 received at 11437 <at> debbugs.gnu.org (full text, mbox):

From: Assaf Gordon <assafgordon <at> gmail.com>
To: Eric Blake <eblake <at> redhat.com>, Samuel Thibault <samuel.thibault <at> gnu.org>
Cc: 11437 <at> debbugs.gnu.org
Subject: Re: bug#11437: coreutils: Please disable misc/nice test on hurd-i386]
Date: Mon, 15 Oct 2018 10:56:17 -0600

severity 11437 wishlist
retitle 11437 nice: tests: please disable on hurd-i386
stop

(triaging old bugs)

On 08/05/12 12:54 PM, Eric Blake wrote:
> On 05/08/2012 12:39 PM, Samuel Thibault wrote:
>>
>> The misc/nice test currently fails on hurd-i386 because the nice support
>> there is not precise enough
[...]

> If you make that fix to Hurd, then the mapping will just work, and
> coreutils will start passing the test.

Some years later, 'misc/nice' still fails on hurd:
https://lists.gnu.org/archive/html/coreutils/2016-11/msg00102.html

So marking this as a "wishlist" item.

-assaf

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