linux-kernel - Re: [PATCH] kmalloc_index optimization(code size & runtime stable)

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Date:   Thu, 16 Apr 2020 20:23:54 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Bernard Zhao <bernard@...o.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel@...o.com
Subject: Re: [PATCH] kmalloc_index optimization(code size & runtime stable)

On Thu, Apr 16, 2020 at 07:03:30PM -0700, Bernard Zhao wrote:
> kmalloc_index inline function code size optimization and runtime
> performance stability optimization. After optimization, the function
> kmalloc_index is more stable, the size will never affecte the function`s
> execution efficiency.
> And follow test data shows that the performance of new optimization
> exceeds the original algorithm when applying for more than 512 Bytes
> (include 512B).And new optimization runtime is more stable than before.

That's all very well and good, but the vast majority of allocations
are less than 512 bytes in size!  Your numbers show that on average,
this patch makes the kernel slower!

>             size        time/Per 100 million times
>                         old fun		new fun with optimise
> 		8	203777		241934
> 		16	245611		409278
> 		32	236384		408419
> 		64	275499		447732
> 		128	354909		416439
> 		256	360472		406598
> 		512	431072		409168
> 		1024	463822		407401