Re: [PATCH net] virtio_net: Account for tx bytes and packets on sending xdp_frames
From: David Ahern <hidden>
Date: 2019-02-05 03:13:25
On 2/4/19 3:53 AM, Jesper Dangaard Brouer wrote:
On Sat, 2 Feb 2019 14:27:26 -0700 David Ahern [off-list ref] wrote:quoted
On 1/31/19 1:15 PM, Jesper Dangaard Brouer wrote:quoted
quoted
David, Jesper, care to chime in where we ended up in that last thread discussion this?IHMO packets RX and TX on a device need to be accounted, in standard counters, regardless of XDP. For XDP RX the packet is counted as RX, regardless if XDP choose to XDP_DROP. On XDP TX which is via XDP_REDIRECT or XDP_TX, the driver that transmit the packet need to account the packet in a TX counter (this if often delayed to DMA TX completion handling). We cannot break the expectation that RX and TX counter are visible to userspace stats tools. XDP should not make these packets invisible.Agreed. What I was pushing on that last thread was Rx, Tx and dropped are all accounted by the driver in standard stats. Basically if the driver touched it, the driver's counters should indicate that.Sound like we all agree (except with the dropped counter, see below). Do notice that mlx5 driver doesn't do this. It is actually rather confusing to use XDP on mlx5, as when XDP "consume" which include XDP_DROP, XDP_REDIRECT or XDP_TX, then the driver standard stats are not incremented... the packet is invisible to "ifconfig" stat based tools.
mlx5 needs some work. As I recall it still has the bug/panic removing xdp programs - at least I don't recall seeing a patch for it.
quoted
The push back was on dropped packets and whether that counter should be bumped on XDP_DROP.My opinion is the XDP_DROP action should NOT increment the drivers drop counter. First of all the "dropped" counter is also use for other stuff, which will confuse that this counter express. Second, choosing XDP_DROP is a policy choice, it still means it was RX-ed at the driver level.
Understood. Hopefully in March I will get some time to come back to this and propose an idea on what I would like to see - namely, the admin has a config option at load time to enable driver counters versus custom map counters. (meaning the operator of the node chooses standard stats over strict performance.) But of course that means the drivers have the code to collect those stats.