RE: [PATCH rdma-next 0/3] Support out of order data placement

Parav Pandit
2017-06-12T16:19:37Z

Hi Bart,

> -----Original Message-----
> From: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org [mailto:linux-rdma-
> owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org] On Behalf Of Bart Van Assche
> Sent: Monday, June 12, 2017 10:28 AM
> To: leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org; dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org
> Cc: linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; Idan Burstein <idanb-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> Subject: Re: [PATCH rdma-next 0/3] Support out of order data placement
>
> On Mon, 2017-06-12 at 09:49 +0300, Leon Romanovsky wrote:
> > Out of order data placement capability indicates that if HCA receives
> > out of order RDMA packets, their data placement can be done at the
> > desired memory destination given in the packet(s). This is applicable
> > to RDMA read and write operations.
>
> Hello Leon and Parav,
>
> Since PCIe writes can be executed out of order, shouldn't that be mentioned
> in Documentation/infiniband/out_of_order.txt? See also the
> documentation of the Device Control Register and the Enable Relaxed
> Ordering bit in the PCIe spec.
There is no change in the way PCIe writes are done with respect to this per QP bit.
Meaning, if this bit is cleared, PCIe subsystem can still do out of order writes depending on relaxed ordering flag.

>
> Additionally, since not handling out-of-order RDMA writes correctly is an
> ULP bug and since there are more ULPs that handle out-of-order writes
> correctly than ULPs that don't handle out-of-order writes correctly, if a new
> flag is introduced, shouldn't that be a flag to disable out-of-order writes?
Not sure I understood correctly. This bit is not a bug fix for ULPs who don't handle out-of-order writes.
As I described in Documentation,
" Out of order data placement capability indicates that if HCA receives out of order RDMA packets, their data placement can be done at the desired memory destination given in the packet(s). This is applicable to RDMA read and write operations."
This flag indicates that - in above condition, HCA can do data placement out-of-order.
Without enabling this flag, when HCA receives out of order packets, it would drop them due to PSN sequence error.

So, - to your question - shouldn't that be a flag to disable out-of-order writes?
By default, its disabled at RDMA level.

>
> Thanks,
>
> Bart.--
> To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the
> body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info
> at http://vger.kernel.org/majordomo-info.html