On 11/01/17 14:58, Joonas Lahtinen wrote:
On ke, 2017-01-11 at 12:14 +0000, Chris Wilson wrote:
When switching between contexts using the aliasing_ppgtt, the VM is
shared. We don't need to reload the PD registers unless they are dirty.
Martin Peres reported an issue that looks like corruption between
Haswell context switches, bisecting to commit f9326be5f1d3 ("drm/i915:
Rearrange switch_context to load the aliasing ppgtt on first use").
Switching between the same mm (the aliasing_ppgtt is used for all
contexts in this case) should be a nop, but appears to trigger some
side-effects in the context switch. However, as we know the switch
is redundant in this case, we can skip it and continue to ignore the
issue until somebody feels strong enough to investigate full-ppgtt on
gen7 again!
Fixes: f9326be5f1d3 ("drm/i915: Rearrange switch_context to load the aliasing ppgtt on first use")
Reported-by: Martin Peres <martin.peres@xxxxxxxxxxxxxxx>
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Martin Peres <martin.peres@xxxxxxxxxxxxxxx>
Code looks good, could use the T-b's to verify.
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Regards, Joonas
https://cgit.freedesktop.org/~ickle/linux-2.6/commit/?h=for-mupuf&id=cfe8f1043b45896af23e4a978020fe20e90c5072
was actually the commit that massively improved the corruption I was
seeing in one benchmark while this patch had no visible impact.
However, my problem was that i915.enable_ppgtt=2 was set in
/etc/modprobe.d/... and I had completely forgotten about it.
So yeah, now you know that f9326be5f1d3 massively broke enable_ppgtt=2,
but not sure what you want to do about it.
There is no hurry though, as the defaults are sane.
Sorry for the noise everyone, I hope that my painful manual bisects will
be useful if someone wants to make the second mode work :)
Martin
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