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From: Nathan Bossart <[email protected]>
To: [email protected] <[email protected]>
Cc: John Naylor <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: David Rowley <[email protected]>
Cc: [email protected] <[email protected]>
Cc: [email protected] <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: [PATCH] Hex-coding optimizations using SVE on ARM.
Date: Wed, 10 Sep 2025 22:12:52 -0500
Message-ID: <aMI-NF6KLc1x1pko@nathan> (raw)
In-Reply-To: <OS9PR01MB15185B278E343A9BA5F0F6AB19700A@OS9PR01MB15185.jpnprd01.prod.outlook.com>
References: <OSBPR01MB266437C48E1F5ACB3D8C69C197E12@OSBPR01MB2664.jpnprd01.prod.outlook.com>
	<Z5VguuGPybo5ai_S@nathan>
	<TY2PR01MB26671195A71369185F7BD08C97F42@TY2PR01MB2667.jpnprd01.prod.outlook.com>
	<OSBPR01MB2664ED032A81FBF21BEC82EE97C52@OSBPR01MB2664.jpnprd01.prod.outlook.com>
	<aEBOVMM2TrXJ948v@nathan>
	<OS9PR01MB15185A8BA8E15E4AFD8B14490976BA@OS9PR01MB15185.jpnprd01.prod.outlook.com>
	<OS9PR01MB15185626CA7C6EAF82C93ABA3974FA@OS9PR01MB15185.jpnprd01.prod.outlook.com>
	<TY4PR01MB15177710A7DF163A8536F26289701A@TY4PR01MB15177.jpnprd01.prod.outlook.com>
	<CANWCAZZm4zwAFmy6M32Sj2BfDg8ZjEV4TJ0YwBQewjV=AUY1Qw@mail.gmail.com>
	<OS9PR01MB15185B278E343A9BA5F0F6AB19700A@OS9PR01MB15185.jpnprd01.prod.outlook.com>

On Thu, Sep 04, 2025 at 02:55:50PM +0000, [email protected] wrote:
>> I see that there was some discussion about a Neon implementation upthread,
>> but I'm not sure we concluded anything.  For popcount, we first added a
>> Neon version before adding the SVE version, which required more complicated
>> configure/runtime checks.  Presumably Neon is available on more hardware
>> than SVE, so that could be a good place to start here, too.
> 
> We have added the Neon versions of hex encode/decode.

Thanks.  I noticed that this stuff is simple enough that we can use
port/simd.h (with a few added functions).  This is especially nice because
it takes care of x86, too.  The performance gains look similar to what you
reported for v6:

                arm
    buf  | HEAD  | patch | % diff
  -------+-------+-------+--------
      16 |    13 |     6 |   54
      64 |    34 |     9 |   74
     256 |    93 |    25 |   73
    1024 |   281 |    78 |   72
    4096 |  1086 |   227 |   79
   16384 |  4382 |   927 |   79
   65536 | 17455 |  3608 |   79

                x86
    buf  | HEAD  | patch | % diff
  -------+-------+-------+--------
      16 |    10 |     7 |   30
      64 |    29 |     9 |   69
     256 |    81 |    21 |   74
    1024 |   286 |    66 |   77
    4096 |  1106 |   253 |   77
   16384 |  4383 |   980 |   78
   65536 | 17491 |  3886 |   78

I've only modified hex_encode() for now, but I'm optimistic that we can do
something similar for hex_decode().

-- 
nathan


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