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Re: [PATCH v2] Improve performance of strstr
On Fri, Apr 12, 2019 at 04:49:11PM +0000, Wilco Dijkstra wrote:
> Hi Szabolcs,
>
> > please cc those who previously had objections against
> > the patch and ask if they sustain their objections
> > and if so what changes or demonstrations are needed
> > to move this forward.
>
> I haven't seen any constructive objections nor received any reply
> when I asked for actual evidence of a claimed regression [1].
I have already explained to you the cases which are going to perform
pathologically bad with your vaguely optimized version of the naive
O(nm) strstr. I don't have your specific hardware to run benchmarks,
but the order of magnitude here is so large that a big-O argument
suffices. If the proposed size limit were something like 24 or 32
rather than 256 that might not necessarily be the case.
I vaguely recall doing some testing on a glibc x86_64 box that showed
the magnitude of the problem; I can try to dig that up or do it again
if you really want to see it.
Rich