Another Test Run with Alternative pmap Implementation

[Svatopluk Kraus]

Thanks for explanation. In this case, however, wrapping by sched_pin() and
sched_unpin() calls would be enough. Nevertheless, as our pmap is based on
i386 one, I asked Alan Cox for the meaning of this warning and created
patch according to his answer.

More about PCPU stuff could be found in [1].  ;)

Svata

[1]
http://lists.freebsd.org/pipermail/freebsd-current/2013-February/039858.html



On Fri, Nov 28, 2014 at 6:50 PM, Adrian Chadd <adrian at freebsd.org> wrote:

> Hi,
>
> PCPU_GET()ed things aren't atomic. Unless you're in a critical
> section, you can be pre-empted at any time and migrated to another
> CPU. There aren't explicit "migration points" that kernel code can be
> migrated - it can be pre-empted and migrated to other CPUs whenever
> something else at a higher priority comes along.
>
> So if you're not wrapping your PCPU_GET() and subsequent work inside a
> critical section - if you're using the PCPU_GET()'ed data outside of
> the critical section, then you're in for a world of trouble.
>
>
>
> -adrian
>
>
> On 28 November 2014 at 01:31, Svatopluk Kraus <onwahe at gmail.com> wrote:
> > I think that the pmap_remove_page warning is very likely due to not
> atomic
> > PCPU_GET(). Can you please try attached patch.
> >
> > Svata
> >
> >
> >
> > On Thu, Nov 27, 2014 at 6:09 PM, Ian Lepore <ian at freebsd.org> wrote:
> >
> >> On Wed, 2014-11-26 at 22:18 +0000, Weiß, Dr. Jürgen wrote:
> >> > I made a testrun with the updated source tree and the patches for
> >> > the jetson tk1 platform. With
> >> >
> >> > options               ARM_NEW_PMAP
> >> > options         DEBUG
> >> > options         DIAGNOSTIC
> >> > options         INVARIANTS              # Enable calls of extra sanity
> >> checking
> >> > options         INVARIANT_SUPPORT       # Extra sanity checks of
> >> internal structures, required by INVARIAN
> >> >
> >> > and no special sysctl settings.
> >> >
> >> > A make -j6 buildworld finishes successfully after 2h15m. There is
> >> > one kernel message
> >> > kernel: warning: pmap_remove_pages called with non-current pmap
> >> >
> >> > /usr/src and /usr/obj over nfs, /tmp on tmpfs
> >> >
> >> > Regards
> >>
> >> That's similar to my results.  I changed to -j20 to see if that would
> >> recreate the problems that Ulrich is seeing, but buildworld runs fine
> >> for me, in about 2 hours.  I've never seen the non-current pmap warning
> >> on the system that uses a usb ssd drive as root, but I've seen it with
> >> nfs root.
> >>
> >> BTW, the DIAGNOSTIC option adds a LOT of performance overhead to an arm
> >> system without adding a lot of value.  I usually leave it off, sometimes
> >> turn it on when I encounter a problem to see if it generates more info
> >> (usually it doesn't).
> >>
> >> -- Ian
> >>
> >>
> >>
> >
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