From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 01ADBC282C0 for ; Wed, 23 Jan 2019 23:42:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B1D0421872 for ; Wed, 23 Jan 2019 23:41:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lixom-net.20150623.gappssmtp.com header.i=@lixom-net.20150623.gappssmtp.com header.b="V5kM8us6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727009AbfAWXl6 (ORCPT ); Wed, 23 Jan 2019 18:41:58 -0500 Received: from mail-it1-f196.google.com ([209.85.166.196]:35482 "EHLO mail-it1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726235AbfAWXl5 (ORCPT ); Wed, 23 Jan 2019 18:41:57 -0500 Received: by mail-it1-f196.google.com with SMTP id p197so1845504itp.0 for ; Wed, 23 Jan 2019 15:41:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=lixom-net.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=mvXFbasy0KxJM4oUz3E4CVPaZ2aAQL9LoekKdZeuEn0=; b=V5kM8us6izsZVg7y0ePyVsfkkHkw2wTAs/4GLXIg4gRUBqaB+DwQ+c61lQgEnDwf5w n+2pCsd840/UgkO8tlFFlH7V1ogiU6MShYfBT1Oja0Ur71C9If98XapdRhCSAEBGyg+P WBzbbWC4CytiuaW0dHJ95TJv6S23usRhjLT7PzKyTFWxohygQbz3JWeTMtbqx3krwCLQ FQEG4zHR0zrlNc/4EfT4Q+Ar8haA8AuHHaY8PTnz8sEp9UekSp5tkigZi1eZZMK0WIc3 6tP52tgsxNmk4Egs0CsLx6+HRrA+g/6E5GnMxwCbGKq8+KHl5rkNCHAYxps5QwUFNhdl KwMg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=mvXFbasy0KxJM4oUz3E4CVPaZ2aAQL9LoekKdZeuEn0=; b=Jn6MPFXjB/G27SihWnOa5Ij71ouk9ssemquasmH8PtGTZdnN8pNi/GnL8v8Wq+MqIy MPLNZnkLfzGTYFXFM3yMwg+soqzW80nE72UfYN7teTfQDU9dhVyuxfKudogvPk+hIPW0 JCZFas5Cmm8jZD/U28T7Un5Be+LlgGUz3aaZhHvfku5ZiBaEd5L33K/MKGP3uA4NKVx4 yMuPh4DOhTPJoiQExLV0HNEfVbhZErJ+b1exy6NcqiED7CJFALa2V5xWVORUFwq/IdmV yH2YcAgyE8sf7tTrzAXSiVR4O/C4n1zT3DyMIbS2SSvG4cd3VCUf4v1nGbN5bAfPzMAZ t5YQ== X-Gm-Message-State: AJcUukey+RufpyE0iqOj2VK4mbKSNpVkSq30yrppY0RIRZDcGdeu80PI Heopfj0kQU2cGOmwnM8OPkPEZsc9/x6Ldz1xsjYcsA== X-Google-Smtp-Source: ALg8bN7Ihps31c2yhVHOQXYtHFfI6aQ9OVSXSNqHPcJlsQcPyTOKejjQbrYMgq9CfDolMugkQ5rvG8DmwcuvEUlYPi8= X-Received: by 2002:a02:89dd:: with SMTP id e29mr3064676jak.21.1548286916412; Wed, 23 Jan 2019 15:41:56 -0800 (PST) MIME-Version: 1.0 References: <20190123000057.31477-1-oded.gabbay@gmail.com> <20190123232052.GD1257@redhat.com> In-Reply-To: From: Olof Johansson Date: Wed, 23 Jan 2019 15:41:45 -0800 Message-ID: Subject: Re: [PATCH 00/15] Habana Labs kernel driver To: Oded Gabbay Cc: Jerome Glisse , Dave Airlie , Greg Kroah-Hartman , Daniel Vetter , LKML , ogabbay@habana.ai, Arnd Bergmann , fbarrat@linux.ibm.com, Andrew Donnellan Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 23, 2019 at 3:35 PM Oded Gabbay wrote: > > On Thu, Jan 24, 2019 at 1:20 AM Jerome Glisse wrote: > > > > On Wed, Jan 23, 2019 at 03:04:33PM -0800, Olof Johansson wrote: > > > On Wed, Jan 23, 2019 at 2:45 PM Dave Airlie wrote: > > > > > > > > On Thu, 24 Jan 2019 at 08:32, Oded Gabbay wrote: > > > > > > > > > > On Thu, Jan 24, 2019 at 12:02 AM Dave Airlie wrote: > > > > > > > > > > > > Adding Daniel as well. > > > > > > > > > > > > Dave. > > > > > > > > > > > > On Thu, 24 Jan 2019 at 07:57, Dave Airlie wrote: > > > > > > > > > > > > > > On Wed, 23 Jan 2019 at 10:01, Oded Gabbay wrote: > > > > > > > > > > > > > > > > Hello, > > > > > > > > > > > > > > > > For those who don't know me, my name is Oded Gabbay (Kernel Maintainer > > > > > > > > for AMD's amdkfd driver, worked at RedHat's Desktop group) and I work at > > > > > > > > Habana Labs since its inception two and a half years ago. > > > > > > > > > > > > > > Hey Oded, > > > > > > > > > > > > > > So this creates a driver with a userspace facing API via ioctls. > > > > > > > Although this isn't a "GPU" driver we have a rule in the graphics > > > > > > > drivers are for accelerators that we don't merge userspace API with an > > > > > > > appropriate userspace user. > > > > > > > > > > > > > > https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#open-source-userspace-requirements > > > > > > > > > > > > > > I see nothing in these accelerator drivers that make me think we > > > > > > > should be treating them different. > > > > > > > > > > > > > > Having large closed userspaces that we have no insight into means we > > > > > > > get suboptimal locked for ever uAPIs. If someone in the future creates > > > > > > > an open source userspace, we will end up in a place where they get > > > > > > > suboptimal behaviour because they are locked into a uAPI that we can't > > > > > > > change. > > > > > > > > > > > > > > Dave. > > > > > > > > > > Hi Dave, > > > > > While I always appreciate your opinion and happy to hear it, I totally > > > > > disagree with you on this point. > > > > > > > > > > First of all, as you said, this device is NOT a GPU. Hence, I wasn't > > > > > aware that this rule might apply to this driver or to any other driver > > > > > outside of drm. Has this rule been applied to all the current drivers > > > > > in the kernel tree with userspace facing API via IOCTLs, which are not > > > > > in the drm subsystem ? I see the logic for GPUs as they drive the > > > > > display of the entire machine, but this is an accelerator for a > > > > > specific purpose, not something generic as GPU. I just don't see how > > > > > one can treat them in the same way. > > > > > > > > The logic isn't there for GPUs for those reason that we have an > > > > established library or that GPUs are in laptops. They are just where > > > > we learned the lessons of merging things whose primary reason for > > > > being in the kernel is to execute stuff from misc userspace stacks, > > > > where the uAPI has to remain stable indefinitely. > > > > > > > > a) security - without knowledge of what the accelerator can do how can > > > > we know if the API you expose isn't just a giant root hole? > > > > > > > > b) uAPI stability. Without a userspace for this, there is no way for > > > > anyone even if in possession of the hardware to validate the uAPI you > > > > provide and are asking the kernel to commit to supporting indefinitely > > > > is optimal or secure. If an open source userspace appears is it to be > > > > limited to API the closed userspace has created. It limits the future > > > > unnecessarily. > > > > > > > > > There is no way that "someone" will create a userspace > > > > > for our H/W without the intimate knowledge of the H/W or without the > > > > > ISA of our programmable cores. Maybe for large companies this request > > > > > is valid, but for startups complying to this request is not realistic. > > > > > > > > So what benefit does the Linux kernel get from having support for this > > > > feature upstream? > > > > > > > > If users can't access the necessary code to use it, why does this > > > > require to be maintained in the kernel. > > > > > > > > > To conclude, I think this approach discourage other companies from > > > > > open sourcing their drivers and is counter-productive. I'm not sure > > > > > you are aware of how difficult it is to convince startup management to > > > > > opensource the code... > > > > > > > > Oh I am, but I'm also more aware how quickly startups go away and > > > > leave the kernel holding a lot of code we don't know how to validate > > > > or use. > > > > > > > > I'm opening to being convinced but I think defining new userspace > > > > facing APIs is a task that we should take a lot more seriously going > > > > forward to avoid mistakes of the past. > > > > > > I think the most important thing here is to know that things are > > > likely to change quite a bit over the next couple of years, and that > > > we don't know yet what we actually need. If we hold off picking up > > > support for hardware while all of this is ironed out, we'll miss out > > > on being exposed to it, and will have a very tall hill to climb once > > > we try to convince vendors to come into the fold. It's also not been a > > > requirement for the other two drivers we have merged, as far as I can > > > tell (CAPI and OpenCAPI) so the cat's already out of the bag. > > > > > > I'd rather not get stuck in a stand-off needing the longterm solution > > > to pick up the short term contribution. That way we can move over to a > > > _new_ API once there's been a better chance of finding common grounds > > > and once things settle down a bit, instead of trying to bring some > > > larger legacy codebase for devices that people might no longer care > > > much about over to the newer APIs. > > > > > > It's better to be exposed to the HW and drivers now, than having > > > people build large elaborate out-of-tree software stacks for this. > > > It's also better to get them to come and collaborate now, instead of > > > pushing them away until things are perfect. > > > > > > Having a way to validate and exercise the userspace API is important, > > > including ability to change it if needed. Would it be possible to open > > > up the lowest userspace pieces (driver interactions), even if some > > > other layers might not yet be, to exercise the device/kernel/userspace > > > interfaces without "live" workload, etc? > > > > Yes and to exercise the userspace API you need at very least to > > know the ISA so that you can write program for the accelerator. > > You also need to know the set of commands the hardware has. The > > ioctl and how to create a userspace that interact with the kernel > > is the easy part, the hard part is the compiler. > > So actually in my case in order to exercise the IOCTL API, you can > give "work" to the device that will not trigger the compute parts, but > only the different queues and the DMA engines. > I think that is enough to validate that the IOCTLs won't break. > All the "commands" that you can give to the queue logic (QMAN) is > exposed in one of the files in the driver (goya_packets.h). > > I want to stress this - To validate the IOCTLs, it is enough to do DMA > work. You will use ALL the 5 IOCTLs to do just that - give work to the > DMA engines. I personally think this is a reasonable trade-off, given that you have a communication layer between. For hardware that doesn't have that, and where device behavior and data movement depends on execution on the compute parts, more would need to be open. -Olof