Re: rdma_create_qp() and max_send_wr

[Yann Droneaud <ydroneaud-RlY5vtjFyJ3QT0dZR+AlfA@public.gmane.org>]

Hi,

Le jeudi 19 mai 2011 à 18:59 +0200, Yann Droneaud a écrit :
> Le jeudi 19 mai 2011 à 18:46 +0300, Eli Cohen a écrit :
> > On Thu, May 19, 2011 at 05:03:45PM +0200, Yann Droneaud wrote:
> > > 
> > > To sum up:
> > > 
> > > - ibv_qp_init_attr.max_recv_wr can be set to ibv_device_attr.max_qp_wr,
> > > 16384 in my case,
> > >  
> > > - ibv_qp_init_attr.max_send_wr *cannot* be set to
> > > ibv_device_attr.max_qp_wr, but it can be set to 16351.
> > > 
> > Thanks for investigating this. We'll check and send a fix. Meanwhile
> > you can workaround this in your code.
> 
> I understand the problem (which is probably not really a problem):
> 
> In libmlx4/src/verbs.c:mlx4_create_qp()
> 
>         mlx4_calc_sq_wqe_size(&attr->cap, attr->qp_type, qp);
> 
>         /*
>          * We need to leave 2 KB + 1 WQE of headroom in the SQ to
>          * allow HW to prefetch.
>          */

This was introduced by commit 561da8d1

Handle new FW requirement for send request prefetching

http://git.kernel.org/?p=libs/infiniband/libmlx4.git;a=commit;h=561da8d1

Regards.

-- 
Yann Droneaud
OPTEYA



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