Skip site navigation (1)Skip section navigation (2)
Date:      Fri, 28 Nov 2014 09:50:23 -0800
From:      Adrian Chadd <adrian@freebsd.org>
To:        Svatopluk Kraus <onwahe@gmail.com>
Cc:        "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org>, Ian Lepore <ian@freebsd.org>
Subject:   Re: Another Test Run with Alternative pmap Implementation
Message-ID:  <CAJ-Vmok=yN4EqMucLCz=ZkoUv8pGnp8FHTzLo%2BTuXFE2_K1CMg@mail.gmail.com>
In-Reply-To: <CAFHCsPWL94b5JFL87__MxGfGFrA4q0c3QgPwZf7MGzJ9i6hsaQ@mail.gmail.com>
References:  <20141113125236.b16cd4e5f0e339eac0494cd4@ulrich-grey.de> <C6FED1A5-490C-47BE-B071-484271ED370E@me.com> <20141115143444.5ad037548e06f289d2532fb7@ulrich-grey.de> <CAFHCsPUJ1HhLqAjitPg6mPzhMYSui64Xmu4omO7Pkp%2B0kPZnAA@mail.gmail.com> <20141119225903.81fbbc7809093a0e6e0de9d5@ulrich-grey.de> <CAFHCsPXnSFY_X-O73M%2Bh0xO_XJ0cTmkRwtu-o4omPndnfbEhmg@mail.gmail.com> <20141120151900.a68c6d8316b96a62cb65d17a@ulrich-grey.de> <CAFHCsPWTnU7j0MC7YSHFFDE97%2B%2BBrnkJKGnK9zkxVGemaa6nAw@mail.gmail.com> <20141121115941.54d4e36b103341c3adf7eb36@ulrich-grey.de> <20141124132733.4e96b906f0d1ab69969dddd9@ulrich-grey.de> <1416840814.1147.380.camel@revolution.hippie.lan> <20141125225451.924a5df4bdb4753db273b8c5@ulrich-grey.de> <CAFHCsPXPEN3U%2B0=AtAJ4dL5g7jGuyW6=u%2B-tbHf3xH1QdJYyhQ@mail.gmail.com> <20141126125806.78f2df97328e807d12746ae3@ulrich-grey.de> <519fde5db60e4fc594956a600c6cad4e@e15be-01.zdv.Uni-Mainz.DE> <1417108193.1055.2.camel@revolution.hippie.lan> <CAFHCsPWL94b5JFL87__MxGfGFrA4q0c3QgPwZf7MGzJ9i6hsaQ@mail.gmail.com>

next in thread | previous in thread | raw e-mail | index | archive | help
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@gmail.com> wrote:
> I think that the pmap_remove_page warning is very likely due to not atomi=
c
> PCPU_GET(). Can you please try attached patch.
>
> Svata
>
>
>
> On Thu, Nov 27, 2014 at 6:09 PM, Ian Lepore <ian@freebsd.org> wrote:
>
>> On Wed, 2014-11-26 at 22:18 +0000, Wei=C3=9F, Dr. J=C3=BCrgen 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
>>
>>
>>
>
> _______________________________________________
> freebsd-arm@freebsd.org mailing list
> http://lists.freebsd.org/mailman/listinfo/freebsd-arm
> To unsubscribe, send any mail to "freebsd-arm-unsubscribe@freebsd.org"



Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAJ-Vmok=yN4EqMucLCz=ZkoUv8pGnp8FHTzLo%2BTuXFE2_K1CMg>