Re: [PATCH 5/5] RDMA/srp: Make struct scsi_cmnd and struct srp_request adjacent

[Leon Romanovsky <leonro@mellanox.com>]

On Tue, May 11, 2021 at 08:27:52PM -0700, Bart Van Assche wrote:
> Define .init_cmd_priv and .exit_cmd_priv callback functions in struct
> scsi_host_template. Set .cmd_size such that the SCSI core allocates
> per-command private data. Use scsi_cmd_priv() to access that private
> data. Remove the req_ring pointer from struct srp_rdma_ch since it is
> no longer necessary. Convert srp_alloc_req_data() and srp_free_req_data()
> into functions that initialize one instance of the SRP-private command
> data. This is a micro-optimization since this patch removes several
> pointer dereferences from the hot path.
> 
> Note: due to commit e73a5e8e8003 ("scsi: core: Only return started requests
> from scsi_host_find_tag()"), it is no longer necessary to protect the
> completion path against duplicate responses.
> 
> Cc: Nicolas Morey-Chaisemartin <nmoreychaisemartin@suse.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  drivers/infiniband/ulp/srp/ib_srp.c | 156 ++++++++++++----------------
>  drivers/infiniband/ulp/srp/ib_srp.h |   2 -
>  2 files changed, 65 insertions(+), 93 deletions(-)
> 
> diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
> index 52db42af421b..773ac5929082 100644
> --- a/drivers/infiniband/ulp/srp/ib_srp.c
> +++ b/drivers/infiniband/ulp/srp/ib_srp.c
> @@ -965,69 +965,55 @@ static void srp_disconnect_target(struct srp_target_port *target)
>  	}
>  }
>  
> -static void srp_free_req_data(struct srp_target_port *target,
> -			      struct srp_rdma_ch *ch)
> +static int srp_exit_cmd_priv(struct Scsi_Host *shost, struct scsi_cmnd *cmd)
>  {
> +	struct srp_target_port *target = host_to_target(shost);
>  	struct srp_device *dev = target->srp_host->srp_dev;
>  	struct ib_device *ibdev = dev->dev;
> -	struct srp_request *req;
> -	int i;
> +	struct srp_request *req = scsi_cmd_priv(cmd);
>  
> -	if (!ch->req_ring)
> -		return;
> -
> -	for (i = 0; i < target->req_ring_size; ++i) {
> -		req = &ch->req_ring[i];
> -		if (dev->use_fast_reg)
> -			kfree(req->fr_list);
> -		if (req->indirect_dma_addr) {
> -			ib_dma_unmap_single(ibdev, req->indirect_dma_addr,
> -					    target->indirect_size,
> -					    DMA_TO_DEVICE);
> -		}
> -		kfree(req->indirect_desc);
> +	if (dev->use_fast_reg)
> +		kfree(req->fr_list);

Isn't cleaner will be to ensure that fr_list is NULL for !dev->use_fast_reg path?
In patch #4 https://lore.kernel.org/linux-rdma/20210512032752.16611-5-bvanassche@acm.org

Thanks