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Re: Performance requirements for Unicode views/types/algorithms

From: Tom Honermann <tom_at_[hidden]>
Date: Tue, 28 Feb 2023 14:50:57 -0500
On 2/28/23 1:43 PM, Jens Maurer via SG16 wrote:
> On 28/02/2023 16.18, Niall Douglas via SG16 wrote:
>> On 26/02/2023 01:48, Steve Downey via SG16 wrote:
>>> Much text processing is tied to IO and the performance is mostly
>>> secondary. If we could make accidentally incorrect harder to do that
>>> would be a win.
>> My consumer hardware storage here does 14Gb/sec reads (two PCIe 4.0 SSDs
>> in RAID0). Only a few years ago that was main memory speeds for a high
>> end PC.
>> I think you need to assume text processing, and especially Unicode
>> parsing, is basically main memory speeds whether it is from i/o or not.
>> I really wish SIMD had better support for UTF-8, only AVX-512 enables a
>> decent fraction of main memory bandwidth
>> (https://github.com/simdutf/simdutf).
> Thanks for the pointer. I was looking for a comparison like that.
> So, this means we do leave 5-10x performance on the table if we
> go for an interface that can deliver ICU-level performance (only).
> Sadness engulfs me.
>> I'd like to see as much of that
>> performance passed through by the standard library as possible, even if
>> it makes the API non-STL-like.
> So, it seems we need an idea how to employ SIMD with a ranges-based
> interface, or we go for eager transcoding algorithms (possibly
> in addition to the ranges-based ones).

The interfaces JeanHeyd is proposing for C in WG14 N3095 (Restartable
Functions for Efficient Character Conversions)
<https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3095.htm> are
intended to support implementation with SIMD. As a worst case fallback,
that should be an option if/once it is adopted and deployed.


> Jens

Received on 2023-02-28 19:51:01