Re: [Xen-devel] [PATCH] xen/list: Remove prefetching

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Jan 14, 2020 at 08:35:45PM +0000, Andrew Cooper wrote:
> Xen inherited its list infrastructure from Linux.  One area where has fallen
> behind is that of prefetching, which as it turns out is a performance penalty
> in most cases.
> 
> Prefetch of NULL on x86 is now widely measured to have glacial performance
> properties, and will unconditionally hit on every hlist use due to the
> termination condition.
> 
> Cross-port the following Linux patches:
> 
>   75d65a425c (2011) "hlist: remove software prefetching in hlist iterators"
>   e66eed651f (2011) "list: remove prefetching from regular list iterators"
>   c0d15cc7ee (2013) "linked-list: Remove __list_for_each"
> 
> to Xen, which results in the following net diffstat on x86:
> 
>   add/remove: 0/1 grow/shrink: 27/83 up/down: 576/-1648 (-1072)
> 
> (The code additions comes from a few now-inlined functions, and slightly
> different basic block padding.)
> 
> No functional change.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Has this gone through some XenRT performance testing to assert there
are not regressions performance wise?

Thanks, Roger.

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