On Tue, 2019-06-18 at 14:55 +0300, Artem Bityutskiy wrote: > From: Artem Bityutskiy <artem.bityuts...@linux.intel.com> > > This patch adds the RR2DCDELAY register to the ethtool registers dump. > RR2DCDELAY exists on I210 and I211 Intel Gigabit Ethernet chips and it stands > for "Read Request To Data Completion Delay". Here is how this register is > described in the I210 datasheet: > > "This field captures the maximum PCIe split time in 16 ns units, which is the > maximum delay between the read request to the first data completion. This is > giving an estimation of the PCIe round trip time." > > In other words, whenever I210 reads from the host memory (e.g., fetches a > descriptor from the ring), the chip measures every PCI DMA read transaction > and > captures the maximum value. So it ends up containing the longest DMA > transaction time. > > This register is very useful for troubleshooting and research purposes. If you > are dealing with time-sensitive networks, this register can help you get > an idea of your "I210-to-ring" latency. This helps answering questions like > "should I have PCIe ASPM enabled?" or "should I enable deep C-states?" on > my system. > > It is safe to read this register at any point, reading it has no effect on > the I210 chip functionality. > > Signed-off-by: Artem Bityutskiy <artem.bityuts...@linux.intel.com> > --- > drivers/net/ethernet/intel/igb/e1000_regs.h | 2 ++ > drivers/net/ethernet/intel/igb/igb_ethtool.c | 5 ++++- > 2 files changed, 6 insertions(+), 1 deletion(-) >
Tested-by: Aaron Brown <aaron.f.br...@intel.com>
