After upgrading the kernel to v4.19 we started seeing increased packet latency on two machines with ASUS H87M-E motherboards with on-board Realtek Gigabit Ethernet. This didn't happen with v4.18. (More details, including kernel log and lspci output at https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=925496 )
Bisecting revealed that commit a99790bf5c7f3d68d8b01e015d3212a98ee7bd57 r8169: Reinstate ASPM Support provoked this change in behaviour. If I patch v4.9.31's drivers/net/ethernet/realtek/r8169.c rtl_hw_aspm_clkreq_enable function to never enable the clocks (which, AFAICT, is equivalent to reverting the aforementioned commit) then packet latency is normal. The increased packet latency can also be resolved by: 1. Running 'ethtool -C eth0 rx-usecs 0 rx-frames 1' 2. Disabling "EPU Power Saving Mode" in the BIOS (on the Ai Tweaker page.) This option is enabled when the "ASUS Optimal" setting is selected on the BIOS front page. but neither of these solutions are ideal because they require the user to realise that there's a problem and discover these solutions. Is there a way to fix the code to work correctly with this motherboard even with "EPU Power Saving Mode" enabled? Thanks. Mike.
