[ovs-dev] [PATCH v5] Detailed packet drop statistics per dpdk and vhostuser ports

Ilya Maximets i.maximets at samsung.com
Tue Aug 6 16:32:16 UTC 2019

On 24.07.2019 11:55, Sriram Vatala wrote:
> Hi,
> @Ben : Thanks for the response.
> @Ilya, @Ian : Can you please review the patch and provide comments if any.

Thanks for working on this!

One thing about the patch is that it modifies the hot path, thus needs
a performance evaluation before applying. I hope to have some time for
it this week. Have you tested performance difference with and without
this patch?

Also, I see is that you're inserting fairly big array into PADDED_MEMBERS
block. There are few issues with that:

1. There is no need to store the whole 'struct netdev_custom_counter' for
   each netdev instance because names takes 64 bytes each and they are
   same for each netdev instance anyway.

2. You're not paying attention to the amount of pad bytes in this section
   after the change. I suspect a big hole in the structure here.

   Regarding this issue, actually, I'd like to remove this cacheline
   alignments completely from the structure (it had no performance impact
   for me previously), but it's a different change and there was no active
   support from the community when I wanted to do that few years ago.
   However, there was no strong objections too.
   Ian, do you have some thought about this?

Best regards, Ilya Maximets.

> Thanks,
> Sriram.
> -----Original Message-----
> From: Ben Pfaff <blp at ovn.org> 
> Sent: 22 July 2019 21:37
> To: Sriram Vatala <sriram.v at altencalsoftlabs.com>
> Cc: ovs-dev at openvswitch.org
> Subject: Re: [PATCH v5] Detailed packet drop statistics per dpdk and
> vhostuser ports
> On Mon, Jul 22, 2019 at 03:31:53PM +0530, Sriram Vatala wrote:
>> OVS may be unable to transmit packets for multiple reasons and today 
>> there is a single counter to track packets dropped due to any of those 
>> reasons. The most common reason is that a VM is unable to read packets 
>> fast enough causing the vhostuser port transmit queue on the OVS side 
>> to become full. This manifests as a problem with VNFs not receiving 
>> all packets. Having a separate drop counter to track packets dropped 
>> because the transmit queue is full will clearly indicate that the 
>> problem is on the VM side and not in OVS. Similarly maintaining 
>> separate counters for all possible drops helps in indicating sensible 
>> cause for packet drops.
>> This patch adds counters for custom stats to track packets dropped at 
>> port level and these stats are displayed along with other stats in 
>> "ovs-vsctl get interface <iface> statistics"
>> command. The detailed stats will be available for both dpdk and 
>> vhostuser ports.
>> Signed-off-by: Sriram Vatala <sriram.v at altencalsoftlabs.com>
> Thanks for the revision!  I'm happy with the bits that are important to me.
> I'll leave the final review to Ian or Ilya.

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