Re: blktest/rxe almost working

[Bob Pearson <rpearsonhpe@gmail.com>]

On 9/7/21 11:39 AM, Jason Gunthorpe wrote:
> On Tue, Sep 07, 2021 at 11:35:17AM -0500, Bob Pearson wrote:
> 
>> Interesting. But if that is the case the bigger problem is the ib_map_mr_sg() call which updates the
>> mapping. rxe definitely does look at the mr->rkey value but we could fix that. It also looks at the
>> mapping which is updated by ib_map_mr_sg(). My impression is that HW also uses this mapping or does
>> HW also copy all the FMRs into SRAM?
> 
> Yes, real HW has a copy of the DMA list. The sg in the mr struct is
> for CPU use only.
> 
> It is not OK to use the CPU SG list inside the MR for DMA by HW, it
> has to be synchronized with the WR.
> 
>> There seems to be an assumption that users will be looking at CQE.
> 
> Yes, the kernel has to be driven by CQE, not only for data transfer
> but the DMA unmap of the SGL cannot be until after the invalidation
> CQE is observed.
> 
> Ie the CPU should have two DMA lists active during the invalidation
> cycle.
> 
> Jason
> 

OK. Not 100% sure what that implies for SRP. SRP does *not* look at the CQE for invalidate and register
WQEs. I can fix the rkey and DMA list semantics, making a copy of the list which is installed by the
register WQE.