Re: [PATCH 03/25] um/xor: don't override XOR_SELECT_TEMPLATE

On Thu, 2026-02-26 at 22:45 +0100, Richard Weinberger wrote:

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quoted

Von: "hch" [off-list ref]
XOR_SELECT_TEMPLATE is only ever called with a NULL argument, so all the
ifdef'ery doesn't do anything.  With our without this, the time travel
mode should work fine on CPUs that support AVX2, as the AVX2
implementation is forced in this case, and won't work otherwise.

IIRC Johannes added XOR_SELECT_TEMPLATE() here to skip
the template selection logic because it didn't work with time travel mode.

Johannes, can you please test whether this change does not break
time travel mode?

It does work, even if it reports nonsense (as you'd expect):

xor: measuring software checksum speed
   prefetch64-sse  : 12816000 MB/sec
   sse             : 12816000 MB/sec
xor: using function: prefetch64-sse (12816000 MB/sec)

I think it works now because the loop is using ktime and is bounded by
REPS, since commit c055e3eae0f1 ("crypto: xor - use ktime for template
benchmarking").

The RAID speed select still hangs, but we've gotten that removed via
Kconfig, so that's already handled. Perhaps raid6_choose_gen() should
use a similar algorithm? But for UML it doesn't really matter since
CONFIG_RAID6_PQ_BENCHMARK exists.


As far as AVX2 is concerned, yeah, I guess that was a bug, but evidently
nobody (who configured time-travel) ever cared - what _did_ matter
though in practice is that the boot not get stuck entirely... Two
completely separate issues.

johannes