Subject: Re: [PATCH 0/2] ixgbe, fix numa issues

From: Alexander Duyck <[email-masked]>
Date: Mon, 24 Feb 2014 11:23:42 -0800

On 02/24/2014 10:51 AM, Prarit Bhargava wrote:
> The ixgbe driver makes some assumptions about the layout of cpus in the
> system which are not always correct given a particular system layout.  The
> ixgbe driver allocates one MSI/cpu for queue usage but the code does not take
> into account that devices are located on NUMA nodes and that the cpus in a node
> are not contiguous.
>
> These issues were found while doing cpu hotplug testing, however, both of these
> issues can lead to obvious system performance issues as they defeat the
> purpose of having one MSI processing a queue per cpu.
>
> Cc: Jeff Kirsher <[email-masked]>
> Cc: Jesse Brandeburg <[email-masked]>
> Cc: Bruce Allan <[email-masked]>
> Cc: Carolyn Wyborny <[email-masked]>
> Cc: Don Skidmore <[email-masked]>
> Cc: Greg Rose <[email-masked]>
> Cc: Alex Duyck <[email-masked]>
> Cc: John Ronciak <[email-masked]>
> Cc: Mitch Williams <[email-masked]>
> Cc: "David S. Miller" <[email-masked]>
> Cc: [email-masked]
> Cc: [email-masked]
> Cc: [email-masked]
>
> Prarit Bhargava (2):
>   ixgbe, make interrupt allocations NUMA aware
>   ixgbe, don't assume mapping of numa node cpus
>
>  drivers/net/ethernet/intel/ixgbe/ixgbe.h       |    2 ++
>  drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c   |   44 ++++++++++++++++++------
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c  |    6 ++--
>  drivers/net/ethernet/intel/ixgbe/ixgbe_sriov.c |    5 +--
>  4 files changed, 42 insertions(+), 15 deletions(-)
>

This is a step in the right direction but totally defeats the purpose of
ATR.  With this change we might as well defeature ATR all together since
things are now back to RSS w/ NUMA specific allocations which is what we
had a couple of years ago.  The code as it is written now would be a
better for for igb which doesn't have ATR than ixgbe.

ATR is supposed to map 1:1 queues to CPUs.  The problem is RSS is also a
factor and not especially smart or NUMA aware.  The ideal solution would
be to allocate the first N CPUs, where N is the number in the local node
for ATR/RSS.  Then map all other queues as ATR with a 1:1 mapping to CPUs.

Thanks,

Alex