Re: Debian kernel boot failure on Alpha [was Re: systemd FTBFS]
On Wed, Mar 29, 2017 at 01:41:29PM +0200, Frank Scheiner wrote:
> I have had a similar problem than you, i.e. no generic Linux kernel v4.x
> from Debian runs or ran on my Alpha gear (the newest one is a PWS 500au with
> EV56).
I seem to recall the last working kernel is v4.2. Interestingly the
Debian generic kernel boots my Titian variant alpha but not the XP1000.
> The older 3.16.x kernel worked without a problem on my machines though.
> Hence I thought that maybe something was changed in the v4.x kernels that
> made them incompatible with pre EV6 CPUs.
The XP1000 is ev67 and the generic kernel fails to boot on it.
> There were some messages about
> enabling BWX (starting with [1]), but as it should still work with EV56 when
> enabled I wondered if my problems were related at all.
>
> [1]: https://lists.debian.org/debian-alpha/2014/09/msg00000.html
>
> Mid of 2015 you wrote on [2] that you haven't yet enabled BWX,
I've managed to switch the defaults in gcc in a test run and started
a local repository rebuild to test it but it exposed a nasty bug in libc
so I couldn't continue to test. That took some time to fix and I never
returned to exploring switching Debian Ports to using BWX. My feeling is
that we should in fact do that considering that the i386 arch recently
dropped support for Intel chips that are more recent than the old-time
Alpha cpus we still support!
> Until recently I didn't have a reason to also try the SMP variant of the
> v4.x Linux kernels, but now that I have a DS20E and had the same problems
> with the generic Linux kernel v4.x from Debian I also tried the SMP variant
> on it.
>
> And the SMP variant of the v4.x kernel just works (tested with
> "4.8.0.2-alpha-smp", "Debian 4.8.11-1" from 2016-12-02 to be exact).
Now that it is interesting! The SMP kernel also boots on my XP1000.
The only downside to using an SMP kernel is extra allocations of per-cpu
data structures, and the loss of some optimised code that eject SMP
barriers.
I would be wary of using the Debian 4.9 kernel for any serious work on
Alpha. I presume it still has commit
0784672d05684de901fc2aa56150d7ea9a475a2d which leads to random
segfaults in user space on Alpha (and the occasional kernel OOPS).
Cheers
Michael.
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