Date: Sun, 15 Nov 2015 13:55:01 +0100
From: Christoph Hellwig <hch@lst.de>
To: Sagi Grimberg <sagig@dev.mellanox.co.il>
Cc: Christoph Hellwig <hch@lst.de>, linux-rdma@vger.kernel.org,
        bart.vanassche@sandisk.com, axboe@fb.com, linux-scsi@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/9] IB: add a proper completion queue abstraction
Message-ID: <20151115125501.GB2218@lst.de>
References: <1447422410-20891-1-git-send-email-hch@lst.de> <1447422410-20891-3-git-send-email-hch@lst.de> <564852F2.5080602@dev.mellanox.co.il>
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On Sun, Nov 15, 2015 at 11:40:02AM +0200, Sagi Grimberg wrote:
> I doubt INT_MAX is useful as a budget in any use-case. it can easily
> hog the CPU. If the consumer is given access to poll a CQ, it must be
> able to provide some way to budget it. Why not expose a budget argument
> to the consumer?

Because in theory we could have a lot of sends completing before
we finally need to reap them.  I think that's more of a theoretical
than real issue.

My preference would be to simply kill this mode though.  Allocate a IU
to each block request in SRP and only use the free_tx list for task
management and AEN/req_limit calls.  Then we can use a single CQ
and mark the regular I/O requests as unsignalled.

AFAICS no other driver wants a similar polling mode as the SRP initiator
does for it's send queue.
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