Re: [igt-dev] [PATCH i-g-t 3/4] i915/gem_shrink: Refactor allocation sizing based on available memory

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 14/12/2020 10:51, Chris Wilson wrote:
> Refactor the allocation such that we utilise just enough memory pressure
> to invoke the shrinker, and just enough processes to spread across the
> CPUs and contend on the shrinker.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   tests/i915/gem_shrink.c | 11 ++++++-----
>   1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/tests/i915/gem_shrink.c b/tests/i915/gem_shrink.c
> index 023db8c56..e8a814fe6 100644
> --- a/tests/i915/gem_shrink.c
> +++ b/tests/i915/gem_shrink.c
> @@ -426,6 +426,7 @@ igt_main
>   	int num_processes = 0;
>   
>   	igt_fixture {
> +		const int ncpus = sysconf(_SC_NPROCESSORS_ONLN);
>   		uint64_t mem_size = intel_get_total_ram_mb();
>   		int fd;
>   
> @@ -434,16 +435,16 @@ igt_main
>   
>   		/*
>   		 * Spawn enough processes to use all memory, but each only
> -		 * uses half the available mappable aperture ~128MiB.
> +		 * uses half of the available per-cpu memory.
>   		 * Individually the processes would be ok, but en masse
>   		 * we expect the shrinker to start purging objects,
>   		 * and possibly fail.
>   		 */
> -		alloc_size = gem_mappable_aperture_size(fd) / 2;
> -		num_processes = 1 + (mem_size / (alloc_size >> 20));
> +		alloc_size = (mem_size + ncpus - 1) / ncpus / 2;

Div round up with thousands divided by small integers okay, safe on very 
old smp boxes. :)

> +		num_processes = ncpus + (mem_size / alloc_size);

Hm, now what does this add up to..

ncpus + mem_size / (mem_size / ncpus / 2) = ... ?

Regards,

Tvrtko

>   
> -		igt_info("Using %d processes and %'lluMiB per process\n",
> -			 num_processes, (long long)(alloc_size >> 20));
> +		igt_info("Using %d processes and %'"PRIu64"MiB per process\n",
> +			 num_processes, alloc_size);
>   
>   		intel_require_memory(num_processes, alloc_size,
>   				     CHECK_SWAP | CHECK_RAM);
> 
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