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Date: Wed, 1 May 2019 13:04:09 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Tal Gilboa <talgi@...lanox.com>
Cc: linux-rdma@...r.kernel.org, linux-nvme@...ts.infradead.org,
linux-block@...r.kernel.org, Yishai Hadas <yishaih@...lanox.com>,
Leon Romanovsky <leon@...nel.org>,
Doug Ledford <dledford@...hat.com>,
Tariq Toukan <tariqt@...lanox.com>,
Saeed Mahameed <saeedm@...lanox.com>,
Idan Burstein <idanb@...lanox.com>,
Yamin Friedman <yaminf@...lanox.com>,
Max Gurtovoy <maxg@...lanox.com>,
"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH rdma-for-next 0/9] drivers/infiniband: Introduce rdma_dim
On Wed, May 01, 2019 at 05:44:30PM +0300, Tal Gilboa wrote:
> net_dim.h lib exposes an implementation of the DIM algorithm for dynamically-tuned interrupt
> moderation for networking interfaces.
>
> We want a similar functionality for RDMA. The main motivation is to benefit from maximized
> completion rate and reduced interrupt overhead that DIM may provide.
>
> Current DIM implementation prioritizes reducing interrupt overhead over latency. Also, in
> order to reduce DIM's own overhead, the algorithm might take take some time to identify it
> needs to change profiles. For these reasons we got to the understanding that a slightly
> modified algorithm is needed. Early tests with current implementation show it doesn't react
> fast and sharply enough in order to satisfy the RDMA CQ needs.
>
> I would like to suggest an implementation for RDMA DIM. The idea is to expose the new
> functionality without the risk of breaking Net DIM behavior for netdev. Below are main
> similarities and differences between the two implementations and general guidelines for the
> suggested solution.
>
> Performance improvement (ConnectX-5 100GbE, x86) running FIO benchmark over
> NVMf between two equal end-hosts with 56 cores across a Mellanox switch
> using null_blk device:
>
> READS without DIM:
> blk size | BW | IOPS | 99th percentile latency | 99.99th latency
> 512B | 3.8GiB/s | 7.7M | 1401 usec | 2442 usec
> 4k | 7.0GiB/s | 1.8M | 4817 usec | 6587 usec
> 64k | 10.7GiB/s| 175k | 9896 usec | 10028 usec
>
> IO WRITES without DIM:
> blk size | BW | IOPS | 99th percentile latency | 99.99th latency
> 512B | 3.6GiB/s | 7.5M | 1434 usec | 2474 usec
> 4k | 6.3GiB/s | 1.6M | 938 usec | 1221 usec
> 64k | 10.7GiB/s| 175k | 8979 usec | 12780 usec
>
> IO READS with DIM:
> blk size | BW | IOPS | 99th percentile latency | 99.99th latency
> 512B | 4GiB/s | 8.2M | 816 usec | 889 usec
> 4k | 10.1GiB/s| 2.65M| 3359 usec | 5080 usec
> 64k | 10.7GiB/s| 175k | 9896 usec | 10028 usec
>
> IO WRITES with DIM:
> blk size | BW | IOPS | 99th percentile latency | 99.99th latency
> 512B | 3.9GiB/s | 8.1M | 799 usec | 922 usec
> 4k | 9.6GiB/s | 2.5M | 717 usec | 1004 usec
> 64k | 10.7GiB/s| 176k | 8586 usec | 12256 usec
>
> Common logic, main DIM procedure:
> - Calculate current stats from a given sample
> - Compare current stats vs. previous iteration stats
> - Make a decision -> choose a new profile
>
> Differences:
> - Different parameters for moving between profiles
> - Different moderation values and number of profiles
> - Different sampled data
>
> Suggested solution:
> - Common logic will be declared in include/linux/dim.h and implemented in lib/dim/dim.c
> - Net DIM (existing) logic will be declared in include/linux/net_dim.h and implemented in
> lib/dim/net_dim.c, which will use the common logic from dim.h
> - RDMA DIM logic will be declared in /include/linux/rdma_dim.h and implemented in
> lib/dim/rdma_dim.c.
> This new implementation will expose modified versions of profiles, dim_step() and dim_decision()
>
> Pros for this solution are:
> - Zero impact on existing net_dim implementation and usage
> - Relatively more code reuse (compared to two separate solutions)
> - Readiness for future implementations
>
> Tal Gilboa (6):
> linux/dim: Move logic to dim.h
> linux/dim: Remove "net" prefix from internal DIM members
> linux/dim: Rename externally exposed macros
> linux/dim: Rename net_dim_sample() to net_dim_create_sample()
> linux/dim: Rename externally used net_dim members
> linux/dim: Move implementation to .c files
>
> Yamin Friedman (3):
> linux/dim: Add completions count to dim_sample
> linux/dim: Implement rdma_dim
> drivers/infiniband: Use rdma_dim in infiniband driver
>
> MAINTAINERS | 3 +
> drivers/infiniband/core/cq.c | 79 ++++-
> drivers/infiniband/hw/mlx4/qp.c | 2 +-
> drivers/infiniband/hw/mlx5/qp.c | 2 +-
> drivers/net/ethernet/broadcom/bcmsysport.c | 20 +-
> drivers/net/ethernet/broadcom/bcmsysport.h | 2 +-
> drivers/net/ethernet/broadcom/bnxt/bnxt.c | 13 +-
> drivers/net/ethernet/broadcom/bnxt/bnxt.h | 2 +-
> drivers/net/ethernet/broadcom/bnxt/bnxt_debugfs.c | 4 +-
> drivers/net/ethernet/broadcom/bnxt/bnxt_dim.c | 7 +-
> drivers/net/ethernet/broadcom/genet/bcmgenet.c | 18 +-
> drivers/net/ethernet/broadcom/genet/bcmgenet.h | 2 +-
> drivers/net/ethernet/mellanox/mlx5/core/en.h | 8 +-
> drivers/net/ethernet/mellanox/mlx5/core/en_dim.c | 12 +-
> .../net/ethernet/mellanox/mlx5/core/en_ethtool.c | 4 +-
> drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 22 +-
> drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c | 12 +-
A lot of this is touching netdev, why wasn't netdev cc'd?
Who is supposed to merge this?
I think you need to take two steps and have netdev merge the above
part and then send the single patch to RDMA for the last part, I don't
really want to take so much netdev code here.
The maintainers file should also have some indication which tree
patches for lib/dim/* this should go through..
Jason
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