netdev - RE: [PATCH] ixgbevf - Prevent RX/TX statistics getting reset to zero

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Date:	Fri, 13 Jul 2012 05:36:37 -0700
From:	<Narendra_K@...l.com>
To:	<jeffrey.t.kirsher@...el.com>, <gregory.v.rose@...el.com>
CC:	<netdev@...r.kernel.org>
Subject: RE: [PATCH] ixgbevf - Prevent RX/TX statistics getting reset to zero

> -----Original Message-----
> From: Jeff Kirsher [mailto:tarbal@...il.com]
> Sent: Thursday, July 12, 2012 11:56 PM
> To: K, Narendra; gregory.v.rose@...el.com
> Cc: netdev@...r.kernel.org
> Subject: Re: [PATCH] ixgbevf - Prevent RX/TX statistics getting reset to zero
> 
> On 07/12/2012 06:55 AM, Narendra_K@...l.com wrote:
> > Hello,
> >
> > [Apologies if you are receiving this message twice. I am resending the
> message, as I got message delivery failure note].
> >
> > While exploring SR-IOV on Intel 82599EB 10-Gigabit SFP+ adapter, I had the
> following observation.  I enabled two VFs by passing 'max_vfs=2' to ixgbe
> driver. One of the VFs was assigned to a guest.
> > In the guest, the ifconfig and ip tools reported 'RX packets' and 'TX packets'
> as zero, after pinging to a remote host. Looking into it further, the commit
> 4197aa7bb81877ebb06e4f2cc1b5fea2da23a7bd implements 64 bit per ring
> statistics. It seemed like the 'total_bytes' and 'total_packets' of RX and TX
> ring were being reset to zero by the RX and TX interrupt handlers, resulting in
> the user space tools reporting zero RX and TX bytes.
> >
> > The attached patch addresses the issue by preventing the resetting of RX
> and TX ring statistics to zero. The patch was taken against latest mainline 3.5-
> rc6 kernel.
> >
> > I tested the patch by pinging  from the guest OS to a remote host.
> >
> > ping -f <remote host> -c 10000
> >
> > The ip and ifcofig showed the statistics increased by 10000 packets.
> >
> > # lspci | grep 82599
> > 04:00.0 Ethernet controller: Intel Corporation 82599EB 10-Gigabit SFP+
> Network Connection (rev 01)
> > 04:00.1 Ethernet controller: Intel Corporation 82599EB 10-Gigabit SFP+
> Network Connection (rev 01)
> > 04:10.0 Ethernet controller: Intel Corporation 82599 Ethernet Controller
> Virtual Function (rev 01)
> > 04:10.1 Ethernet controller: Intel Corporation 82599 Ethernet Controller
> Virtual Function (rev 01)
> > 04:10.2 Ethernet controller: Intel Corporation 82599 Ethernet Controller
> Virtual Function (rev 01)
> > 04:10.3 Ethernet controller: Intel Corporation 82599 Ethernet Controller
> Virtual Function (rev 01)
> >
> > # lspci -s 04:00.0 -n
> > 04:00.0 0200: 8086:154d (rev 01)
> > # lspci -s 04:10.0 -n
> > 04:10.0 0200: 8086:10ed (rev 01)
> >
> > Please let me know if additional details and logs are required.[>]  
> >
> > With regards,
> > Narendra K
> >
> >
> >
> 
> Thanks, I will add the patch to my queue
> 
[>] 

Hi Greg,

I was re-looking at why ' rx_ring->total_packets' and ' rx_ring->total_bytes' were being set to zero in ' ixgbevf_msix_clean_rx'.  It looks like ' rx_ring->total_packets' and ' rx_ring->total_packets'  are computed per one run of 'ixgbevf_clean_rx_irq' .  Then in 'ixgbevf_clean_rxonly' if 'adapter->itr_setting & 1' is true, the count is  used in  'ixgbevf_set_itr_msix'. When the interrupts are enabled, the 
' rx_ring->total_packets'  and ' rx_ring->total_bytes' are set to zero so that they can be re-computed in the poll function and  fed to the 'ixgbevf_set_itr_msix'.

This results in statistics reported by 'ip' and 'ifconfig' as zero. The patch addresses the scenario.  But it seems it would change the intended behavior in the scenario  when 'adapter->itr_setting & 1' is true.  It could be addressed by storing the 'total_rx_packets' and 'total_rx_bytes'  computed every time in the poll function in 'struct ixgbevf_adapter' . Then the interrupt handler could reset them to zero instead of resetting  ' rx_ring->total_packets' and  ' rx_ring->total_bytes'.

Also, I observed that  'adapter->itr_setting & 1'  was not true by default.  I tried setting it by 'ethtool  -C eth0 adaptive-rx on', and it returned 'operation not supported'. 

I could be missing something here, please let me know.

With regards,
Narendra K