Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH RFC 3/5] Add KSZ8795 switch driver | Date | Fri, 29 Sep 2017 09:14:26 +0000 |
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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
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