Re: [PATCH] RDMA/srp: Fix support for unpopulated and unbalanced NUMA nodes

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Feb 05, 2021 at 09:14:28AM +0100, Nicolas Morey-Chaisemartin wrote:
> The current code computes a number of channels per SRP target and spreads
> them equally across all online NUMA nodes.
> Each channel is then assigned a CPU within this node.
> 
> In the case of unbalanced, or even unpopulated nodes, some channels
> do not get a CPU associated and thus do not get connected.
> This causes the SRP connection to fail.
> 
> This patch solves the issue by rewriting channel computation and allocation:
> - Drop channel to node/CPU association as it had
>   no real effect on locality but added unnecessary complexity.
> - Tweak the number of channels allocated to reduce CPU contention when possible:
>   - Up to one channel per CPU (instead of up to 4 by node)
>   - At least 4 channels per node, unless ch_count module parameter is used.
> 
> Signed-off-by: Nicolas Morey-Chaisemartin <nmoreychaisemartin@suse.com>
> ---
>  drivers/infiniband/ulp/srp/ib_srp.c | 110 ++++++++++++----------------
>  1 file changed, 45 insertions(+), 65 deletions(-)

Bart?

Jason