lkml.org 
[lkml]   [2021]   [Jul]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 1/3] sfc: revert "reduce the number of requested xdp ev queues"
From
Date
On 08/07/2021 13:14, Íñigo Huguet wrote:
> In my opinion, there is no reason to make that distinction between
> normal traffic and XDP traffic.
> [...]
> If the user wants to prevent XDP from mixing with normal traffic, just
> not attaching an XDP program to the interface, or not using
> XDP_TX/REDIRECT in it would be enough. Probably I don't understand
> what you want to say here.

I think it's less about that and more about avoiding lock contention.
If two sources (XDP and the regular stack) are both trying to use a TXQ,
and contending for a lock, it's possible that the resulting total
throughput could be far less than either source alone would get if it
had exclusive use of a queue.
There don't really seem to be any good answers to this; any CPU in the
system can initiate an XDP_REDIRECT at any time and if they can't each
get a queue to themselves then I don't see how the arbitration can be
performant. (There is the middle-ground possibility of TXQs shared by
multiple XDP CPUs but not shared with the regular stack, in which case
if only a subset of CPUs are actually handling RX on the device(s) with
an XDP_REDIRECTing program it may be possible to avoid contention if
the core-to-XDP-TXQ mapping can be carefully configured.)

-ed

\
 
 \ /
  Last update: 2021-07-09 16:08    [W:0.069 / U:0.400 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site