On Mon, Oct 07, 2019 at 08:07:55AM -0700, Bart Van Assche wrote:
> On 10/7/19 6:59 AM, Leon Romanovsky wrote:
> > /*
> > - * Check if the device might use memory registration. This is currently
> > only
> > - * true for iWarp devices. In the future we can hopefully fine tune this
> > based
> > - * on HCA driver input.
> > + * Check if the device might use memory registration. This is currently
> > + * true for iWarp devices and devices that have optimized SGL registration
> > + * logic.
> > */
>
> The following sentence in the above comment looks confusing to me: "Check if
> the device might use memory registration." That sentence suggests that the
> HCA decides whether or not to use memory registration. Isn't it the RDMA R/W
> code that decides whether or not to use memory registration?
I'm open for any reasonable text, what do you expect to be written there?
>
> > + * For RDMA READs we must use MRs on iWarp and can optionaly use them as an
> > + * optimaztion otherwise. Additionally we have a debug option to force
> > usage
> > + * of MRs to help testing this code path.
>
> You may want to change "optionaly" into "optionally" and "optimaztion" into
> "optimization".
Thanks
>
> > static inline bool rdma_rw_io_needs_mr(struct ib_device *dev, u8 port_num,
> > enum dma_data_direction dir, int dma_nents)
> > {
> > - if (rdma_protocol_iwarp(dev, port_num) && dir == DMA_FROM_DEVICE)
> > - return true;
> > + if (dir == DMA_FROM_DEVICE) {
> > + if (rdma_protocol_iwarp(dev, port_num))
> > + return true;
> > + if (dev->attrs.max_sgl_rd && dma_nents > dev->attrs.max_sgl_rd)
> > + return true;
> > + }
> > if (unlikely(rdma_rw_force_mr))
> > return true;
> > return false;
>
> Should this function be renamed? The function name suggests if this function
> returns 'true' that using memory registration is mandatory. My understanding
> is if this function returns true for the mlx5 HCA that using memory
> registration improves performance but is not mandatory.
The end result the same, better to work with MR while working with mlx5 for
"dma_nents >
dev->attrs.max_sgl_rd",
Thanks
>
> Thanks,
>
> Bart.
