Re: [PATCH] net: ethernet: fs-enet: Use generic CRC32 implementation

On 24 July 2018 at 13:05, David Laight [off-list ref] wrote:

From: Krzysztof Kozlowski

quoted

Sent: 23 July 2018 17:20
Use generic kernel CRC32 implementation because it:
1. Should be faster (uses lookup tables),

Are you sure?
The lookup tables are unlikely to be in the data cache and
the 6 cache misses kill performance.
(Not that it particularly matters when setting up multicast hash tables).

Good point, so this statement should be rather "Could be faster"... I
did not run any performance tests so this is not backed up by any
data.

I think the main benefit is rather easier code maintenance by removing
duplicated, custom code.

quoted

2. Removes duplicated CRC generation code,
3. Uses well-proven algorithm instead of coding it one more time.

...

quoted

Not tested on hardware.

Have you verified that the old and new functions give the
same result for a few mac addresses?
It is very easy to use the wrong bits in crc calculations
or generate the output in the wrong bit order.

I copied the original code and new one onto a different driver and run
this in a loop for thousands of data input (although not all possible
MAC combinations). The output was the same. I agree however that real
testing would be important.

Best regards,
Krzysztof