linux-kernel - Re: Interacting with coherent memory on external devices

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Message-ID: <20150423185240.GO5561@linux.vnet.ibm.com>
Date:	Thu, 23 Apr 2015 11:52:40 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jerome Glisse <j.glisse@...il.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	jglisse@...hat.com, mgorman@...e.de, aarcange@...hat.com,
	riel@...hat.com, airlied@...hat.com,
	aneesh.kumar@...ux.vnet.ibm.com,
	Cameron Buschardt <cabuschardt@...dia.com>,
	Mark Hairgrove <mhairgrove@...dia.com>,
	Geoffrey Gerfin <ggerfin@...dia.com>,
	John McKenna <jmckenna@...dia.com>, akpm@...ux-foundation.org
Subject: Re: Interacting with coherent memory on external devices

On Thu, Apr 23, 2015 at 09:38:15AM -0500, Christoph Lameter wrote:
> On Thu, 23 Apr 2015, Benjamin Herrenschmidt wrote:

[ . . . ]

> > It might not be *your* model based on *your* application but that doesn't mean
> > it's not there, and isn't relevant.
> 
> Sadly this is the way that an entire industry does its thing.

I must confess that I got lost in the pronouns.

If by "this is the way" and "entire industry" you mean hand-tuning
for the former and the specific industry you are in for the latter,
I am with you.  And again, we are not going to do anything that would
prevent hand-tuning.  For example, it will be possible to completely
disable any migration operations that might contribute to OS jitter.
And I have added a requirement that this migration mechanism not
contribute to OS jitter unless it is enabled.  Does that help?

If by "entire industry" you mean everyone who might want to use hardware
acceleration, for example, including mechanical computer-aided design,
I am skeptical.

							Thanx, Paul

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