[x265] [PATCH] Performance: Prevent small thread-pools if NUMA disabled and # CPUs > MAX_POOL_THREADS

[Steve Borho]

On 08/26, pradeep at multicorewareinc.com wrote:
> # HG changeset patch
> # User Pradeep Ramachandran <pradeep at multicorewareinc.com>
> # Date 1440585642 -19800
> #      Wed Aug 26 16:10:42 2015 +0530
> # Node ID dd7ef2bd657f8e8369c2b8c10e0452b9ff6e37f5
> # Parent  d8091487bc9749e702c468786b0cd9e663478a91
> Performance: Prevent small thread-pools if NUMA disabled and # CPUs > MAX_POOL_THREADS
> 
> When NUMA is disabled and if # CPUs is > MAX_POOL_THREADS (64 or 32 depending on 64-bit
> or 32-bit builds), the last pool may have few threads. This patch allows the last pool to
> exist only if it has > MAX_POOL_THREADS/2 threads; the 50% number is a heurstic.
> 
> Feature gains performance of 5% on Intel Xeon E5-2699v3 measured in slower preset with 4K video.

LGTM

> diff -r d8091487bc97 -r dd7ef2bd657f source/common/threadpool.cpp
> --- a/source/common/threadpool.cpp	Tue Aug 25 16:39:12 2015 -0700
> +++ b/source/common/threadpool.cpp	Wed Aug 26 16:10:42 2015 +0530
> @@ -289,6 +289,14 @@
>          }
>      }
>  
> +    // In the case that numa is disabled and we have more CPUs than 64,
> +    // spawn the last pool only if the # threads in that pool is > 1/2 max (heuristic)
> +    if ((numNumaNodes == 1) && (cpusPerNode[0] % MAX_POOL_THREADS < (MAX_POOL_THREADS / 2)))
> +    {
> +        cpusPerNode[0] -= (cpusPerNode[0] % MAX_POOL_THREADS);
> +        x265_log(p, X265_LOG_DEBUG, "Creating only %d worker threads to prevent asymmetry in pools; may not use all HW contexts\n", cpusPerNode[0]);
> +    }
> +
>      numPools = 0;
>      for (int i = 0; i < numNumaNodes; i++)
>      {
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-- 
Steve Borho