On 08/25/2016 12:19 PM, Alexander Duyck wrote:
The problem is that there is no socket associated with the guest from
the host's perspective. This is resulting in the traffic bouncing
between queues because there is no saved socket to lock the interface
onto.
I was looking into this recently as well and had considered a couple
of options. The first is to fall back to just using skb_tx_hash()
when skb->sk is null for a given buffer. I have a patch I have been
toying around with but I haven't submitted it yet. If you would like
I can submit it as an RFC to get your thoughts. The second option is
to enforce the use of RPS for any interfaces that do not perform Rx in
NAPI context. The correct solution for this is probably some
combination of the two as you have to have all queueing done in order
at every stage of the packet processing.
I don't know with interfaces would be hit, but just in general, I'm not
sure that requiring RPS be enabled is a good solution - picking where
traffic is processed based on its addressing is fine in a benchmarking
situation, but I think it is better to have the process/thread scheduler
decide where something should run and not the addressing of the
connections that thread/process is servicing.
I would be interested in seeing the RFC patch you propose.
Apart from that, given the prevalence of VMs these days I wonder if
perhaps simply not enabling XPS by default isn't a viable alternative.
I've not played with containers to know if they would exhibit this too.
Drifting ever so slightly, if drivers are going to continue to enable
XPS by default, Documentation/networking/scaling.txt might use a tweak:
diff --git a/Documentation/networking/scaling.txt
b/Documentation/networking/sca
index 59f4db2..8b5537c 100644
--- a/Documentation/networking/scaling.txt
+++ b/Documentation/networking/scaling.txt
@@ -402,10 +402,12 @@ acknowledged.
==== XPS Configuration
-XPS is only available if the kconfig symbol CONFIG_XPS is enabled (on by
-default for SMP). The functionality remains disabled until explicitly
-configured. To enable XPS, the bitmap of CPUs that may use a transmit
-queue is configured using the sysfs file entry:
+XPS is available only when the kconfig symbol CONFIG_XPS is enabled
+(on by default for SMP). The drivers for some NICs will enable the
+functionality by default. For others the functionality remains
+disabled until explicitly configured. To enable XPS, the bitmap of
+CPUs that may use a transmit queue is configured using the sysfs file
+entry:
/sys/class/net/<dev>/queues/tx-<n>/xps_cpus
The original wording leaves the impression that XPS is not enabled by
default.
rick
