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Date: Wed, 13 Oct 2021 22:01:22 -0700
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From: "Dixit, Ashutosh" <ashutosh.dixit@intel.com>
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Subject: Re: [igt-dev] [PATCH i-g-t 7/7] benchmarks/gem_exec_fault: Add
 softpin mode to support gens with ppgtt
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To: Zbigniew =?ISO-8859-2?Q?Kempczy=F1ski?= <zbigniew.kempczynski@intel.com>
Cc: igt-dev@lists.freedesktop.org, Petri Latvala <petri.latvala@intel.com>
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On Thu, 07 Oct 2021 23:54:32 -0700, Zbigniew Kempczy=F1ski wrote:
>
> +	/*
> +	 * For older gens .alignment =3D 1ull << 63 lead do bind/unbind,
> +	 * what doesn't work for newer gens with ppgtt.
> +	 * For ppgtt case we use reloc allocator which would just assigns
> +	 * new offset for each batch. This way we enforce bind/unbind vma
> +	 * for each execbuf.

So assigning a new offset will cause a new fault-in (bind) but not sure if
it will cause an actual fault-out (unbind). Though I am not sure if there
is actually a way to force it to happen if this doesn't work? Is there a
way to verify that the unbind is actually happening?

Neither I am sure how setting the 'alignment =3D 1ull << 63' caused a fault
out in the older code.

> +	 */
> +	has_ppgtt =3D gem_uses_full_ppgtt(fd);
> +	if (has_ppgtt) {
> +		igt_info("Using softpin mode\n");
> +		intel_allocator_multiprocess_start();
> +	} else {
> +		igt_assert(gem_allows_passing_alignment(fd));

I think this should be igt_require for the test to skip rather than fail.

> +/*
> + * NOTE: Ensure prove locking in the kernel is off, otherwise results
> + * would be inaccurate.
> + */

This is really a debug setting, any such setting (say lockdep, kmemchek
etc.) will affect benchmarks. So not sure if this specifically needs to be
called out.