linux-kernel - RE: [PATCH 3/9] IB: add a helper to safely drain a QP

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Date:	Mon, 16 Nov 2015 13:03:27 -0600
From:	"Steve Wise" <swise@...ngridcomputing.com>
To:	"'Sagi Grimberg'" <sagig@....mellanox.co.il>,
	"'Christoph Hellwig'" <hch@....de>, <linux-rdma@...r.kernel.org>
Cc:	<bart.vanassche@...disk.com>, <axboe@...com>,
	<linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 3/9] IB: add a helper to safely drain a QP

> -----Original Message-----
> From: linux-rdma-owner@...r.kernel.org [mailto:linux-rdma-owner@...r.kernel.org] On Behalf Of Sagi Grimberg
> Sent: Monday, November 16, 2015 12:38 PM
> To: Steve Wise; 'Christoph Hellwig'; linux-rdma@...r.kernel.org
> Cc: bart.vanassche@...disk.com; axboe@...com; linux-scsi@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH 3/9] IB: add a helper to safely drain a QP
> 
> 
> > After looking at the nes driver, I don't see any common way to support drain w/o some serious driver mods.  Since SRP is the
only
> > user, perhaps we can ignore iWARP for this function...
> 
> But iser/isert essentially does it too (and I think xprtrdma will have
> it soon)...
> 
> the modify_qp is invoked from rdma_disconnect() and we do post
> an 'empty' wr to wait for all the flushes to drain (see
> iser_conn_terminate).

That won't work for iWARP.  Is this code new?  I didn't see any errors that would result from this code when I tested iSER over
cxgb4 with the old iwarp support patches.   

Perhaps we need another way to do this?  Like a completion object in the QP that gets triggered when the SQ and RQ become empty
after a transition to ERROR (and CLOSING for iwarp).  Then a core service that just waits until the QP is empty.  Implementation of
this design would hit the providers though since only they know when the flush is completed.

Alternatively, I could enable post-while-in-error support in cxgb4 and ignore the spec in this regard.  But I'd rather not do that.
:)

Steve.

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