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Subject: Re: [PATCH v2] raid6: arm64: add SVE optimized implementation for
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To: Mark Brown <broonie@kernel.org>
Cc: Demian Shulhan <demyansh@gmail.com>, Ard Biesheuvel <ardb@kernel.org>,
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From: Robin Murphy <robin.murphy@arm.com>
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On 16/04/2026 5:47 pm, Mark Brown wrote:
> On Thu, Apr 16, 2026 at 05:26:08PM +0100, Robin Murphy wrote:
> 
>> Unless you've got a CPU with truly big wide vector units that _can't_ be
>> fully utilised by ASMID ops, then SVE is only really offering whatever
>> incidental benefits fall out of smaller code size. However, if you do have
>> those wider vectors, then the cost of correctly saving/restoring the SVE
>> state - of which a userspace benchmark isn't likely to be very
>> representative - is also going to scale up significantly.
> 
> The other case will be when there's some SVE only extension that
> accelerates something that's relevant for the algorithm.  That's not
> really a thing at present but I imagine that we'll run into that at some
> point.

Indeed - I was implicitly thinking in terms of things that _are_ just 
transliterated from NEON to SVE, where the primary gain is stuff like 
predicate loops, but even that _could_ potentially be enough to justify 
an argument in-kernel SVE (using a 128-bit VL to keep the additional 
state/cost to a minimum).

Cheers,
Robin.