Date:	Tue, 15 Jul 2014 17:23:39 +0000
From:	"Bridgman, John" <John.Bridgman@....com>
To:	Dave Airlie <airlied@...il.com>,
	Christian König <deathsimple@...afone.de>
CC:	"Lewycky, Andrew" <Andrew.Lewycky@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"Deucher, Alexander" <Alexander.Deucher@....com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: RE: [PATCH 00/83] AMD HSA kernel driver



>-----Original Message-----
>From: dri-devel [mailto:dri-devel-bounces@...ts.freedesktop.org] On Behalf
>Of Bridgman, John
>Sent: Tuesday, July 15, 2014 1:07 PM
>To: Dave Airlie; Christian König
>Cc: Lewycky, Andrew; linux-kernel@...r.kernel.org; dri-
>devel@...ts.freedesktop.org; Deucher, Alexander; akpm@...ux-
>foundation.org
>Subject: RE: [PATCH 00/83] AMD HSA kernel driver
>
>
>
>>-----Original Message-----
>>From: Dave Airlie [mailto:airlied@...il.com]
>>Sent: Tuesday, July 15, 2014 12:35 AM
>>To: Christian König
>>Cc: Jerome Glisse; Bridgman, John; Lewycky, Andrew; linux-
>>kernel@...r.kernel.org; dri-devel@...ts.freedesktop.org; Deucher,
>>Alexander; akpm@...ux-foundation.org
>>Subject: Re: [PATCH 00/83] AMD HSA kernel driver
>>
>>On 14 July 2014 18:37, Christian König <deathsimple@...afone.de> wrote:
>>>> I vote for HSA module that expose ioctl and is an intermediary with
>>>> the kernel driver that handle the hardware. This gives a single
>>>> point for HSA hardware and yes this enforce things for any hardware
>>manufacturer.
>>>> I am more than happy to tell them that this is it and nothing else
>>>> if they want to get upstream.
>>>
>>> I think we should still discuss this single point of entry a bit more.
>>>
>>> Just to make it clear the plan is to expose all physical HSA capable
>>> devices through a single /dev/hsa device node to userspace.
>>
>>This is why we don't design kernel interfaces in secret foundations,
>>and expect anyone to like them.
>
>Understood and agree. In this case though this isn't a cross-vendor interface
>designed by a secret committee, it's supposed to be more of an inoffensive
>little single-vendor interface designed *for* a secret committee. I'm hoping
>that's better ;)
>
>>
>>So before we go any further, how is this stuff planned to work for
>>multiple GPUs/accelerators?
>
>Three classes of "multiple" :
>
>1. Single CPU with IOMMUv2 and multiple GPUs:
>
>- all devices accessible via /dev/kfd
>- topology information identifies CPU + GPUs, each has "node ID" at top of
>userspace API, "global ID" at user/kernel interface  (don't think we've
>implemented CPU part yet though)
>- userspace builds snapshot from sysfs info & exposes to HSAIL runtime,
>which in turn exposes the "standard" API
>- kfd sets up ATC aperture so GPUs can access system RAM via IOMMUv2 (fast
>for APU, relatively less so for dGPU over PCIE)
>- to-be-added memory operations allow allocation & residency control
>(within existing gfx driver limits) of buffers in VRAM & carved-out system
>RAM
>- queue operations specify a node ID to userspace library, which translates to
>"global ID" before calling kfd
>
>2. Multiple CPUs connected via fabric (eg HyperTransport) each with 0 or
>more GPUs:
>
>- topology information exposes CPUs & GPUs, along with affinity info
>showing what is connected to what
>- everything else works as in (1) above

This is probably a good point to stress that HSA topology is only intended as an OS-independent way of communicating system info up to higher levels of the HSA stack, not as a new and competing way to *manage* system properties inside Linux or any other OS.

>
>3. Multiple CPUs not connected via fabric (eg a blade server) each with 0 or
>more GPUs
>
>- no attempt to cover this with HSA topology, each CPU and associated GPUs
>is accessed independently via separate /dev/kfd instances
>
>>
>>Do we have a userspace to exercise this interface so we can see how
>>such a thing would look?
>
>Yes -- initial IP review done, legal stuff done, sanitizing WIP, hoping for final
>approval this week
>
>There's a separate test harness to exercise the userspace lib calls, haven't
>started IP review or sanitizing for that but legal stuff is done
>
>>
>>Dave.
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