linux-kernel - Re: [PATCH v2] crypto: xor - fix template benchmarking

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Message-ID: <ZqzaMQDswTxVVVIX@gondor.apana.org.au>
Date: Fri, 2 Aug 2024 21:08:01 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Helge Deller <deller@...nel.org>
Cc: linux-crypto@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
	linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org
Subject: Re: [PATCH v2] crypto: xor - fix template benchmarking

On Mon, Jul 08, 2024 at 02:24:52PM +0200, Helge Deller wrote:
> Commit c055e3eae0f1 ("crypto: xor - use ktime for template benchmarking")
> switched from using jiffies to ktime-based performance benchmarking.
> 
> This works nicely on machines which have a fine-grained ktime()
> clocksource as e.g. x86 machines with TSC.
> But other machines, e.g. my 4-way HP PARISC server, don't have such
> fine-grained clocksources, which is why it seems that 800 xor loops
> take zero seconds, which then shows up in the logs as:
> 
>  xor: measuring software checksum speed
>     8regs           : -1018167296 MB/sec
>     8regs_prefetch  : -1018167296 MB/sec
>     32regs          : -1018167296 MB/sec
>     32regs_prefetch : -1018167296 MB/sec
> 
> Fix this with some small modifications to the existing code to improve
> the algorithm to always produce correct results without introducing
> major delays for architectures with a fine-grained ktime()
> clocksource:
> a) Delay start of the timing until ktime() just advanced. On machines
> with a fast ktime() this should be just one additional ktime() call.
> b) Count the number of loops. Run at minimum 800 loops and finish
> earliest when the ktime() counter has progressed.
> 
> With that the throughput can now be calculated more accurately under all
> conditions.
> 
> Fixes: c055e3eae0f1 ("crypto: xor - use ktime for template benchmarking")
> Signed-off-by: Helge Deller <deller@....de>
> Tested-by: John David Anglin <dave.anglin@...l.net>
> 
> v2:
> - clean up coding style (noticed & suggested by Herbert Xu)
> - rephrased & fixed typo in commit message

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt