On Fri, 2020-12-04 at 15:17 -0800, Jakub Kicinski wrote: > On Fri, 04 Dec 2020 13:57:49 -0800 Saeed Mahameed wrote: > > > > option 2) route PTP traffic to a special SQs per ring, this SQ > > > > will > > > > be > > > > PTP port accurate, Normal traffic will continue through regular > > > > SQs > > > > > > > > Pros: Regular non PTP traffic not affected. > > > > Cons: High memory footprint for creating special SQs > > > > > > > > So we prefer (2) + private flag to avoid the performance hit > > > > and > > > > the > > > > redundant memory usage out of the box. > > > > > > Option 3 - have only one special PTP queue in the system. PTP > > > traffic > > > is rather low rate, queue per core doesn't seem necessary. > > > > We only forward ptp traffic to the new special queue but we create > > more > > than one to avoid internal locking as we will utilize the tx > > softirq > > percpu. > > In other words to make the driver implementation simpler we'll have > a pretty basic feature hidden behind a ethtool priv knob and a number > of queues which doesn't match reality reported to user space. Hm.
I look at these queues as a special HW objects to allow the accurate PTP stamping, they piggyback on the reported txqs, so they are transparent, they just increase the memory footprint of each ring. for the priv flags, one of the floating ideas was to use hwtstamp_rx_filters flags: https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/net_tstamp.h#L107 Our hardware timestamps all packets for free whether you request it or not, Currently there is no option to setup "ALL_PTP" traffic in ethtool -T, but we can add this flag as it make sense to be in ethtool -T, thus we could use it in mlx5 to determine if user selected ALL_PTP, then ptp packets will go through this accurate special path. This is not a W/A or an abuse to the new flag, it just means if you select ALL_PTP then a side effect will be our HW will be more accurate for PTP traffic. What do you think ? Regarding reducing to a single special queue, i will discuss with Eran and the Team on Sunday. Thanks, Saeed.
