RE: [PATCH RFC 3/5] Add KSZ8795 switch driver

[David Laight]

From: Andrew Lunn
> Sent: 28 September 2017 20:34
...
> > There are 34 counters.  In normal case using generic bus I/O or PCI to read them
> > is very quick, but the switch is mostly accessed using SPI, or even I2C.  As the SPI
> > access is very slow.
> 
> How slow is it? The Marvell switches all use MDIO. It is probably a
> bit faster than I2C, but it is a lot slower than MMIO or PCI.
> 
> ethtool -S lan0 takes about 25ms.

Is the SPI access software bit-banged?
Doing that with software delays isn't friendly to the rest of the system.
(Hardware guys please note...)

One possibility is to rate-limit the stats reading.
Then an application cannot completely 'hog' the SPI bandwidth.

	David