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From: Bob Pearson <rpearsonhpe@gmail.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Bart Van Assche <bvanassche@acm.org>,
	"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>
Subject: Re: blktest/rxe almost working
Date: Tue, 7 Sep 2021 11:47:57 -0500	[thread overview]
Message-ID: <69f9746e-6989-179e-6fdf-6920722bb712@gmail.com> (raw)
In-Reply-To: <20210907163939.GW1200268@ziepe.ca>

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.

      reply	other threads:[~2021-09-07 16:48 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-02 21:41 Bob Pearson
2021-09-02 23:38 ` Jason Gunthorpe
2021-09-03 22:18   ` Bob Pearson
2021-09-03 23:13     ` Bart Van Assche
2021-09-04 22:30       ` Jason Gunthorpe
2021-09-05 18:02         ` Bob Pearson
2021-09-07 12:01           ` Jason Gunthorpe
2021-09-07 16:35             ` Bob Pearson
2021-09-07 16:39               ` Jason Gunthorpe
2021-09-07 16:47                 ` Bob Pearson [this message]

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