David Miller wrote:
Secondarily, looping over reading all of the registers of the chip
might kill performance since the IO accesses compete with the
normal packet sending/receiving operations.
This can be true of any ethtool sub-ioctl that beats the registers, if
run in a tight loop. PHYs are particularly nasty, because outside of
hardware problems mentioned in the previous email, many phy read
routines contain a metric ton of udelay() and mdelay()s. Now, an
unpriv'd user can cause the kernel to do tons of in-kernel busy-waits,
in effect spinning the CPU at their mercy.
Jeff
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