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=-8.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 2E869C433E0 for ; Wed, 13 Jan 2021 20:31:26 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6FFB322ADF for ; Wed, 13 Jan 2021 20:31:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6FFB322ADF Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ffwll.ch Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 638C26EC49; Wed, 13 Jan 2021 20:31:24 +0000 (UTC) Received: from mail-ot1-x333.google.com (mail-ot1-x333.google.com [IPv6:2607:f8b0:4864:20::333]) by gabe.freedesktop.org (Postfix) with ESMTPS id 4DA746EC46 for ; Wed, 13 Jan 2021 20:31:23 +0000 (UTC) Received: by mail-ot1-x333.google.com with SMTP id j12so3161396ota.7 for ; Wed, 13 Jan 2021 12:31:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=tIsMFN7MCr4VGDfCyHGUybIAT0I8JVPh44VCIgcVMZE=; b=dRqPF7lgAwV9QYrEN9EdsCRFitGqIqiqgraq5idLuQsXYcKjjhpMB1gR+jX2iKPCon LPlyoERUanzORR1tbPMIE9JzNyX0b8idcUeT3TSAS98LVMR/M5QfBQCca80DDZbtwrZx IQlrPfa+Ek+1oTt8y6d/1GhbvRBS5WGS/mzdU= 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=tIsMFN7MCr4VGDfCyHGUybIAT0I8JVPh44VCIgcVMZE=; b=NXa72c8EYEeODzfNHddOpiv67sH7nLa/PdamQnTfVD9xH/WP/UaJuR3+HYq/KFznmN J4p5B8O9T2AhxsV5cynd0BD7HYgbWUPzLVxGqPpI3HYmAAUQC/7nHfJ2Lf5aiUtOJWmR W8laL8xvkckZjgdxGt0AGD4Kh8ouE2cf4K3QJInd4V8LbZG11miUB88q9Rp0DXEG1qD8 oDJO0rkEANNt6KBpgzxH5uizI4b3bKY29o1cYpoBMBz+1CsO9CzFhN61cqu6eTyx1iMm wKVnNv5TYP3TEn24tmksVh96L2rGkeZGjHH5GJb6XYZ6QJIhaWje8ttEffniTWJIY2uZ 8oAw== X-Gm-Message-State: AOAM531Z4A3nVN4DHUNG46LIpBFino792Y3r8KJEOZxkJzR35Qzm3ESw aDgOmvfKei+VmVrn98sZTfYUx3nLhuPnYb9VJz8u8g== X-Google-Smtp-Source: ABdhPJwEPJznspIjbx89aenwU4mYdS2KpjPGht0zVfxnqLQXk3+0hpnQN+v2Y9p0JpfXROzPyTuJlw1/lhsv/9rRRJs= X-Received: by 2002:a9d:ea6:: with SMTP id 35mr2396936otj.188.1610569882541; Wed, 13 Jan 2021 12:31:22 -0800 (PST) MIME-Version: 1.0 References: <20210107030127.20393-1-Felix.Kuehling@amd.com> <6daf9ebc-507e-6e83-04dd-d7c5fc6998d6@amd.com> <20210113165646.GB521755@redhat.com> In-Reply-To: <20210113165646.GB521755@redhat.com> From: Daniel Vetter Date: Wed, 13 Jan 2021 21:31:11 +0100 Message-ID: Subject: Re: [PATCH 00/35] Add HMM-based SVM memory manager to KFD To: Jerome Glisse X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Alex Sierra , "Yang, Philip" , Felix Kuehling , amd-gfx list , dri-devel Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Wed, Jan 13, 2021 at 5:56 PM Jerome Glisse wrote: > On Fri, Jan 08, 2021 at 03:40:07PM +0100, Daniel Vetter wrote: > > On Thu, Jan 07, 2021 at 11:25:41AM -0500, Felix Kuehling wrote: > > > Am 2021-01-07 um 4:23 a.m. schrieb Daniel Vetter: > > > > On Wed, Jan 06, 2021 at 10:00:52PM -0500, Felix Kuehling wrote: > > > >> This is the first version of our HMM based shared virtual memory manager > > > >> for KFD. There are still a number of known issues that we're working through > > > >> (see below). This will likely lead to some pretty significant changes in > > > >> MMU notifier handling and locking on the migration code paths. So don't > > > >> get hung up on those details yet. > > > >> > > > >> But I think this is a good time to start getting feedback. We're pretty > > > >> confident about the ioctl API, which is both simple and extensible for the > > > >> future. (see patches 4,16) The user mode side of the API can be found here: > > > >> https://github.com/RadeonOpenCompute/ROCT-Thunk-Interface/blob/fxkamd/hmm-wip/src/svm.c > > > >> > > > >> I'd also like another pair of eyes on how we're interfacing with the GPU VM > > > >> code in amdgpu_vm.c (see patches 12,13), retry page fault handling (24,25), > > > >> and some retry IRQ handling changes (32). > > > >> > > > >> > > > >> Known issues: > > > >> * won't work with IOMMU enabled, we need to dma_map all pages properly > > > >> * still working on some race conditions and random bugs > > > >> * performance is not great yet > > > > Still catching up, but I think there's another one for your list: > > > > > > > > * hmm gpu context preempt vs page fault handling. I've had a short > > > > discussion about this one with Christian before the holidays, and also > > > > some private chats with Jerome. It's nasty since no easy fix, much less > > > > a good idea what's the best approach here. > > > > > > Do you have a pointer to that discussion or any more details? > > > > Essentially if you're handling an hmm page fault from the gpu, you can > > deadlock by calling dma_fence_wait on a (chain of, possibly) other command > > submissions or compute contexts with dma_fence_wait. Which deadlocks if > > you can't preempt while you have that page fault pending. Two solutions: > > > > - your hw can (at least for compute ctx) preempt even when a page fault is > > pending > > > > - lots of screaming in trying to come up with an alternate solution. They > > all suck. > > > > Note that the dma_fence_wait is hard requirement, because we need that for > > mmu notifiers and shrinkers, disallowing that would disable dynamic memory > > management. Which is the current "ttm is self-limited to 50% of system > > memory" limitation Christian is trying to lift. So that's really not > > a restriction we can lift, at least not in upstream where we need to also > > support old style hardware which doesn't have page fault support and > > really has no other option to handle memory management than > > dma_fence_wait. > > > > Thread was here: > > > > https://lore.kernel.org/dri-devel/CAKMK7uGgoeF8LmFBwWh5mW1k4xWjuUh3hdSFpVH1NBM7K0=edA@mail.gmail.com/ > > > > There's a few ways to resolve this (without having preempt-capable > > hardware), but they're all supremely nasty. > > -Daniel > > > > I had a new idea, i wanted to think more about it but have not yet, > anyway here it is. Adding a new callback to dma fence which ask the > question can it dead lock ? Any time a GPU driver has pending page > fault (ie something calling into the mm) it answer yes, otherwise > no. The GPU shrinker would ask the question before waiting on any > dma-fence and back of if it gets yes. Shrinker can still try many > dma buf object for which it does not get a yes on associated fence. Having that answer on a given fence isn't enough, you still need to forward that information through the entire dependency graph, across drivers. That's the hard part, since that dependency graph is very implicit in the code, and we'd need to first roll it out across all drivers. > This does not solve the mmu notifier case, for this you would just > invalidate the gem userptr object (with a flag but not releasing the > page refcount) but you would not wait for the GPU (ie no dma fence > wait in that code path anymore). The userptr API never really made > the contract that it will always be in sync with the mm view of the > world so if different page get remapped to same virtual address > while GPU is still working with the old pages it should not be an > issue (it would not be in our usage of userptr for compositor and > what not). > > Maybe i overlook something there. tbh I'm never really clear on how much exactly we need, and whether maybe the new pin/unpin api should fix it all. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel