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21 May 2021 09:28:08 -0700 Date: Fri, 21 May 2021 09:20:57 -0700 From: Matthew Brost To: Daniel Vetter Subject: Re: [Intel-gfx] [RFC 2/2] drm/doc/rfc: i915 new parallel submission uAPI plan Message-ID: <20210521162057.GB22003@sdutt-i7> References: <20210518235830.133834-1-matthew.brost@intel.com> <20210518235830.133834-3-matthew.brost@intel.com> <20210519171157.GA5202@sdutt-i7> <20210520151059.GA3416@sdutt-i7> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) 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: intel-gfx , dri-devel , Jason Ekstrand , Mesa Dev , Daniel Vetter , karl@freedesktop.org, Christian =?iso-8859-1?Q?K=F6nig?= Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Thu, May 20, 2021 at 09:44:59PM +0200, Daniel Vetter wrote: > On Thu, May 20, 2021 at 08:10:59AM -0700, Matthew Brost wrote: > > On Thu, May 20, 2021 at 11:54:25AM +0200, Daniel Vetter wrote: > > > On Wed, May 19, 2021 at 7:19 PM Matthew Brost wrote: > > > > > > > > On Wed, May 19, 2021 at 01:10:04PM +0200, Daniel Vetter wrote: > > > > > On Tue, May 18, 2021 at 04:58:30PM -0700, Matthew Brost wrote: > > > > > > Add entry fpr i915 new parallel submission uAPI plan. > > > > > > > > > > > > v2: > > > > > > (Daniel Vetter): > > > > > > - Expand logical order explaination > > > > > > - Add dummy header > > > > > > - Only allow N BBs in execbuf IOCTL > > > > > > - Configure parallel submission per slot not per gem context > > > > > > > > > > > > Cc: Tvrtko Ursulin > > > > > > Cc: Tony Ye > > > > > > CC: Carl Zhang > > > > > > Cc: Daniel Vetter > > > > > > Cc: Jason Ekstrand > > > > > > Signed-off-by: Matthew Brost > > > > > > --- > > > > > > Documentation/gpu/rfc/i915_parallel_execbuf.h | 144 ++++++++++++++++++ > > > > > > Documentation/gpu/rfc/i915_scheduler.rst | 53 ++++++- > > > > > > 2 files changed, 196 insertions(+), 1 deletion(-) > > > > > > create mode 100644 Documentation/gpu/rfc/i915_parallel_execbuf.h > > > > > > > > > > > > diff --git a/Documentation/gpu/rfc/i915_parallel_execbuf.h b/Documentation/gpu/rfc/i915_parallel_execbuf.h > > > > > > new file mode 100644 > > > > > > index 000000000000..8c64b983ccad > > > > > > --- /dev/null > > > > > > +++ b/Documentation/gpu/rfc/i915_parallel_execbuf.h > > > > > > @@ -0,0 +1,144 @@ > > > > > > +#define I915_CONTEXT_ENGINES_EXT_PARALLEL_SUBMIT 2 /* see i915_context_engines_parallel_submit */ > > > > > > + > > > > > > +/* > > > > > > + * i915_context_engines_parallel_submit: > > > > > > + * > > > > > > + * Setup a slot to allow multiple BBs to be submitted in a single execbuf IOCTL. > > > > > > + * Those BBs will then be scheduled to run on the GPU in parallel. Multiple > > > > > > + * hardware contexts are created internally in the i915 run these BBs. Once a > > > > > > + * slot is configured for N BBs only N BBs can be submitted in each execbuf > > > > > > + * IOCTL and this is implict behavior (e.g. the user doesn't tell the execbuf > > > > > > + * IOCTL there are N BBs, the execbuf IOCTL know how many BBs there are based on > > > > > > + * the slots configuration). > > > > > > + * > > > > > > + * Their are two currently defined ways to control the placement of the > > > > > > + * hardware contexts on physical engines: default behavior (no flags) and > > > > > > + * I915_PARALLEL_IMPLICT_BONDS (a flag). More flags may be added the in the > > > > > > + * future as new hardware / use cases arise. Details of how to use this > > > > > > + * interface below above the flags. > > > > > > + * > > > > > > + * Returns -EINVAL if hardware context placement configuration invalid or if the > > > > > > + * placement configuration isn't supported on the platform / submission > > > > > > + * interface. > > > > > > + * Returns -ENODEV if extension isn't supported on the platform / submission > > > > > > + * inteface. > > > > > > + */ > > > > > > +struct i915_context_engines_parallel_submit { > > > > > > + struct i915_user_extension base; > > > > > > + > > > > > > + __u16 engine_index; /* slot for parallel engine */ > > > > > > + __u16 width; /* number of contexts per parallel engine */ > > > > > > + __u16 num_siblings; /* number of siblings per context */ > > > > > > + __u16 mbz16; > > > > > > > > > > Ok the big picture looks reasonable now, the flags still confuse me. > > > > > > > > > > > > > Yea, it is a bit confusing. > > > > > > > > > > +/* > > > > > > + * Default placement behvavior (currently unsupported): > > > > > > + * > > > > > > + * Rather than restricting parallel submission to a single class with a > > > > > > + * logically contiguous placement (I915_PARALLEL_IMPLICT_BONDS), add a mode that > > > > > > + * enables parallel submission across multiple engine classes. In this case each > > > > > > + * context's logical engine mask indicates where that context can placed. It is > > > > > > + * implied in this mode that all contexts have mutual exclusive placement (e.g. > > > > > > + * if one context is running CS0 no other contexts can run on CS0). > > > > > > + * > > > > > > + * Example 1 pseudo code: > > > > > > + * CSX[Y] = engine class X, logical instance Y > > > > > > + * INVALID = I915_ENGINE_CLASS_INVALID, I915_ENGINE_CLASS_INVALID_NONE > > > > > > + * set_engines(INVALID) > > > > > > + * set_parallel(engine_index=0, width=2, num_siblings=2, > > > > > > + * engines=CS0[0],CS0[1],CS1[0],CS1[1]) > > > > > > + * > > > > > > + * Results in the following valid placements: > > > > > > + * CS0[0], CS1[0] > > > > > > + * CS0[0], CS1[1] > > > > > > + * CS0[1], CS1[0] > > > > > > + * CS0[1], CS1[1] > > > > > > + * > > > > > > + * This can also be though of as 2 virtual engines: > > > > > > + * VE[0] = CS0[0], CS0[1] > > > > > > + * VE[1] = CS1[0], CS1[1] > > > > > > + * > > > > > > + * Example 2 pseudo code: > > > > > > + * CS[X] = generic engine of same class, logical instance X > > > > > > + * INVALID = I915_ENGINE_CLASS_INVALID, I915_ENGINE_CLASS_INVALID_NONE > > > > > > + * set_engines(INVALID) > > > > > > + * set_parallel(engine_index=0, width=2, num_siblings=3, > > > > > > + * engines=CS[0],CS[1],CS[2],CS[0],CS[1],CS[2]) > > > > > > + * > > > > > > + * Results in the following valid placements: > > > > > > + * CS[0], CS[1] > > > > > > + * CS[0], CS[2] > > > > > > + * CS[1], CS[0] > > > > > > + * CS[1], CS[2] > > > > > > + * CS[2], CS[0] > > > > > > + * CS[2], CS[1] > > > > > > + * > > > > > > + * > > > > > > + * This can also be though of as 2 virtual engines: > > > > > > + * VE[0] = CS[0], CS[1], CS[2] > > > > > > + * VE[1] = CS[0], CS[1], CS[2] > > > > > > + > > > > > > + * This enables a use case where all engines are created equally, we don't care > > > > > > + * where they are scheduled, we just want a certain number of resources, for > > > > > > + * those resources to be scheduled in parallel, and possibly across multiple > > > > > > + * engine classes. > > > > > > + */ > > > > > > > > > > So I don't really get what this does compared to setting the flag below. > > > > > Is this just about running the batchbuffers the wrong way round, i.e. if > > > > > you have (simplest case) > > > > > > > > > > width=2, num_sibglings=1, engines=CS[0], CS[1] > > > > > > > > > > Then both > > > > > CS[0], CS[1] > > > > > and > > > > > CS[1], CS[0] > > > > > are possible options for running 2 batches? Iow, the backend is allowed to > > > > > run the batchbuffers the wrong way round, which gains us nothing, since we > > > > > assume the batches take equally long and engines interchangeable. There is > > > > > no scheduling scenario where this additional flexibility can help. > > > > > > > > > > Also we don't have flags to select the only available and then specify an > > > > > entire pipe dream about what the non-flag mode does, without an > > > > > implementation. What is this about? > > > > > > > > > > If it's just "because bonded allowed this" then I think we should just > > > > > unceremonously ditch this. Bummer for the nice kerenldoc you wrote, but > > > > > welp. > > > > > > > > > > > > > High level the flags came out of internal discussions how this interface > > > > should look. The default placement behavior is theoretically possible > > > > with execlists but has no use cases. The GuC supports / current use > > > > cases are a subset of what is possible with I915_PARALLEL_IMPLICT_BONDS. > > > > > > > > Argued about for months and this is where we landed. At the end of the > > > > day I think we needed to show that this interface supports more > > > > placement rules than what the GuC supports / current use cases to future > > > > proof this interface. > > > > > > > > For what is it worth it seems kinda backwards that we landed on the > > > > default behavior not being supported in our current stack / HW. > > > > > > Yeah I think that should be inverted, doesn't make sense. > > > > > > What I still don't get (and I've read Tvrtko's reply with the example) > > > is what exactly is the difference between implicit and not implicit > > > mode? Can you do a single example where the only difference is whether > > > this flag is set, and then explain with that what are the actual > > > differences in scheduling options that the backend is allowed to pick > > > for the set of N patches? > > > > > > I'm feeling a bit dense, but I'm really not seeing what's even going on here :-( > > > > > > > > > + > > > > > > +/* > > > > > > + * I915_PARALLEL_IMPLICT_BONDS - Create implict bonds between each context. > > > > > > + * Each context must have the same number sibling and bonds are implictly create > > > > > > + * of the siblings. > > > > > > + * > > > > > > + * All of the below examples are in logical space. > > > > > > + * > > > > > > + * Example 1 pseudo code: > > > > > > + * CS[X] = generic engine of same class, logical instance X > > > > > > + * INVALID = I915_ENGINE_CLASS_INVALID, I915_ENGINE_CLASS_INVALID_NONE > > > > > > + * set_engines(INVALID) > > > > > > + * set_parallel(engine_index=0, width=2, num_siblings=1, > > > > > > + * engines=CS[0],CS[1], flags=I915_PARALLEL_IMPLICT_BONDS) > > > > > > + * > > > > > > + * Results in the following valid placements: > > > > > > + * CS[0], CS[1] > > > > > > + * > > > > > > + * Example 2 pseudo code: > > > > > > + * CS[X] = generic engine of same class, logical instance X > > > > > > + * INVALID = I915_ENGINE_CLASS_INVALID, I915_ENGINE_CLASS_INVALID_NONE > > > > > > + * set_engines(INVALID) > > > > > > + * set_parallel(engine_index=0, width=2, num_siblings=2, > > > > > > + * engines=CS[0],CS[2],CS[1],CS[3], flags=I915_PARALLEL_IMPLICT_BONDS) > > > > > > + * > > > > > > + * Results in the following valid placements: > > > > > > + * CS[0], CS[1] > > > > > > + * CS[2], CS[3] > > > > > > + * > > > > > > + * This can also be though of as 2 virtual engines: > > > > > > + * VE[0] = CS[0], CS[2] > > > > > > + * VE[1] = CS[1], CS[3] > > > > > > + * > > > > > > + * This enables a use case where all engines are not equal and certain placement > > > > > > + * rules are required (i.e. split-frame requires all contexts to be placed in a > > > > > > + * logically contiguous order on the VCS engines on gen11+ platforms). This use > > > > > > + * case (logically contiguous placement, within a single engine class) is > > > > > > + * supported when using GuC submission. Execlist mode could support all possible > > > > > > + * bonding configurations but currently doesn't support this extension. > > > > > > + */ > > > > > > +#define I915_PARALLEL_IMPLICT_BONDS (1<<0) > > > > > > > > > > Does this map to intel_context_set_nopreempt(), so we could implement it > > > > > also in execlist? > > > > > > > > > > > > > intel_context_set_nopreempt is preempt is part of how this would be > > > > implemented for execlists. For GuC submission there is a algorithm > > > > between the i915 and GuC that inserts same preemption points between > > > > each set of N batches. I believe the rules are if context 1 can > > > > preempted the rest of the contexts (2 - N) can safely be preempted. A go > > > > / join algorithm, implemented with semaphores, around the batches > > > > makes sure the i915 adheres to these rules. > > > > > > > > > Also is this just an artifact of the implementation, or is this somehow > > > > > required functionality for userspace, i.e. the workload fails if e.g. GuC > > > > > decides to preempt all LRC of a parallel virtual engine? Of course just > > > > > preempting one is a bit a bug (but execlist I think happily does that). > > > > > > > > > > > > > I think it is part of the implementation / HW limitations. Basically if > > > > N batches are running in parallel if one of the batches gets preempted > > > > it can hang all the other batches even if it gets restarted. Again the > > > > idea behind this is only preempt any of these contexts between each set > > > > of N batches. The GuC has no concept of batches only contexts hence the > > > > aforementioned algorithm to insert same preemption points between each > > > > set of batches. > > > > > > Well backend preempting one but not the other is a bug. I don't think > > > we need to talk about bugs :-) > > > > > > > I think it is more that backend can't preempt each context atomically as these > > are running on independent engines. Let say the backend tries to preempt 2 > > engines at the same time and only 1 responds, now we are broken with certain > > batches. With the algorithm implmented between the i915 and the Guc the GuC will > > try to preempt the first context if that works, all the other contexts can be > > preempted. > > Ah right, we might have a workload with long non-preemptible sections, but > I guess the MI_SEMAPHORE_WAIT can always preempt. So if GuC just tries on > one of these, it will result in tears. > > > > Now wrt a preempt mode in context creation, I think that makes sense. > > > I'm just wondering whether this is correct here in the parallel > > > submission (and why), or is it just an implementation artifact > > > (current backends are buggy if we'd allow them to preempt) or what's > > > going on. > > > > > > If this is just a case of "this is how current backends work, > > > userspace doesn't actually care whether we allow preempt or not" then > > > I think we should just document the behavior and that's it. Adding > > > uapi for an option for which there's not even an implementation isn't > > > great. > > > > > > > I don't think it is a case of 'this is how current backends work...', I think > > user space knows if it is ok for 1 of the batches to preempted and not the > > others without breaking the batches. > > Yeah this makes more sense as an explanation: Currently the backend (guc > or execlist) figure out whether something can be preempted by just trying. > Since we're dealing with N contexts that's a suboptimal approach, and we > need a flag that indicates whether it's worth it or not. > > So makes sense to me to have this. I guess userspace does actually need > both modes for now, depending upon what it's doing? > -Daniel I agree that is makes sense to have - an explict flag saying it isn't safe to preempt one of the N batches by itself or letting the driver do whatever it wants regarding preemption. The current use case is it can't preempt a single batch but it may change going forward. Lastly, there is overhead to non-preempt mid batch feature so being able to turn it off seems reasonable to me. Matt > > > > > Matt > > > > > But if we can actually choose, and userspace wants to, then I'm all > > > fine with this. And we can always move this to a more generic place if > > > other engines need preempt control later on too. > > > > > > Cheers, Daniel > > > > > > > > > > Matt > > > > > > > > > Cheers, Daniel > > > > > > > > > > > +/* > > > > > > + * Do not allow BBs to be preempted mid BB rather insert coordinated preemption > > > > > > + * points on all hardware contexts between each set of BBs. An example use case > > > > > > + * of this feature is split-frame on gen11+ hardware. When using this feature a > > > > > > + * BB must be submitted on each hardware context in the parallel gem context. > > > > > > + * The execbuf2 IOCTL enforces the user adheres to policy. > > > > > > + */ > > > > > > +#define I915_PARALLEL_NO_PREEMPT_MID_BATCH (1<<1) > > > > > > +#define __I915_PARALLEL_UNKNOWN_FLAGS (-(I915_PARALLEL_NO_PREEMPT_MID_BATCH << 1)) > > > > > > + __u64 flags; /* all undefined flags must be zero */ > > > > > > + __u64 mbz64[3]; /* reserved for future use; must be zero */ > > > > > > + > > > > > > + /* > > > > > > + * width (i) * num_siblings (j) in length > > > > > > + * index = j + i * num_siblings > > > > > > + */ > > > > > > + struct i915_engine_class_instance engines[0]; > > > > > > +} __attribute__ ((packed)); > > > > > > + > > > > > > diff --git a/Documentation/gpu/rfc/i915_scheduler.rst b/Documentation/gpu/rfc/i915_scheduler.rst > > > > > > index 7faa46cde088..64c539486ee4 100644 > > > > > > --- a/Documentation/gpu/rfc/i915_scheduler.rst > > > > > > +++ b/Documentation/gpu/rfc/i915_scheduler.rst > > > > > > @@ -82,4 +82,55 @@ https://spec.oneapi.com/level-zero/latest/core/api.html#ze-command-queue-priorit > > > > > > > > > > > > New parallel submission uAPI > > > > > > ============================ > > > > > > -Details to come in a following patch. > > > > > > +The existing bonding uAPI is completely broken with GuC submission because > > > > > > +whether a submission is a single context submit or parallel submit isn't known > > > > > > +until execbuf time activated via the I915_SUBMIT_FENCE. To submit multiple > > > > > > +contexts in parallel with the GuC the context must be explictly registered with > > > > > > +N contexts and all N contexts must be submitted in a single command to the GuC. > > > > > > +These interfaces doesn't support dynamically changing between N contexts as the > > > > > > +bonding uAPI does. Hence the need for a new parallel submission interface. Also > > > > > > +the legacy bonding uAPI is quite confusing and not intuitive at all. > > > > > > + > > > > > > +The new parallel submission uAPI consists of 3 parts: > > > > > > + > > > > > > +* Export engines logical mapping > > > > > > +* A 'set_parallel' extension to configure contexts for parallel > > > > > > + submission > > > > > > +* Extend execbuf2 IOCTL to support submitting N BBs in a single IOCTL > > > > > > + > > > > > > +Export engines logical mapping > > > > > > +------------------------------ > > > > > > +Certain use cases require BBs to be placed on engine instances in logical order > > > > > > +(e.g. split-frame on gen11+). The logical mapping of engine instances can change > > > > > > +based on fusing. Rather than making UMDs be aware of fusing, simply expose the > > > > > > +logical mapping with the existing query engine info IOCTL. Also the GuC > > > > > > +submission interface currently only supports submitting multiple contexts to > > > > > > +engines in logical order which is a new requirement compared to execlists. > > > > > > +Lastly, all current platforms have at most 2 instances and the logical order is > > > > > > +the same a uABI order. This will change on platforms with more than 2 instances. > > > > > > + > > > > > > +A single bit will be added to drm_i915_engine_info.flags indicating that the > > > > > > +logical instance has been returned and a new field, > > > > > > +drm_i915_engine_info.logical_instance, returns the logical instance. > > > > > > + > > > > > > +A 'set_parallel' extension to configure contexts for parallel submission > > > > > > +------------------------------------------------------------------------ > > > > > > +The 'set_parallel' extension configures a slot for parallel submission of N BBs. > > > > > > +It is setup step that should be called before using any of the contexts. See > > > > > > +I915_CONTEXT_ENGINES_EXT_LOAD_BALANCE or I915_CONTEXT_ENGINES_EXT_BOND for > > > > > > +similar existing examples. Once a slot is configured for parallel submission the > > > > > > +execbuf2 IOCTL can be called submiting N BBs in a single IOCTL. Initially only > > > > > > +support GuC submission. Execlist support can be added later if needed. > > > > > > + > > > > > > +Add I915_CONTEXT_ENGINES_EXT_PARALLEL_SUBMIT and > > > > > > +i915_context_engines_parallel_submit to the uAPI to implement this extension. > > > > > > + > > > > > > +Extend execbuf2 IOCTL to support submitting N BBs in a single IOCTL > > > > > > +------------------------------------------------------------------- > > > > > > +Contexts that have been configured with the 'set_parallel' extension are allowed > > > > > > +to submit N BBs in a single execbuf2 IOCTL. The BBs are either the last N > > > > > > +objects in the drm_i915_gem_exec_object2 list or the first N if > > > > > > +I915_EXEC_BATCH_FIRST is set. The number of BBs is implict based on the slot > > > > > > +submitted and how it has been configured by 'set_parallel' or other extensions. > > > > > > +No uAPI changes in the execbuf IOCTL but worth mentioning the new behavior of > > > > > > +the IOCTL. > > > > > > -- > > > > > > 2.28.0 > > > > > > > > > > > > _______________________________________________ > > > > > > Intel-gfx mailing list > > > > > > Intel-gfx@lists.freedesktop.org > > > > > > https://lists.freedesktop.org/mailman/listinfo/intel-gfx > > > > > > > > > > -- > > > > > Daniel Vetter > > > > > Software Engineer, Intel Corporation > > > > > http://blog.ffwll.ch > > > > > > > > > > > > -- > > > Daniel Vetter > > > Software Engineer, Intel Corporation > > > http://blog.ffwll.ch > > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch 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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 2D062C47078 for ; Fri, 21 May 2021 16:28:12 +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 C53BE613AF for ; Fri, 21 May 2021 16:28:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C53BE613AF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=intel-gfx-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id C28E56F596; Fri, 21 May 2021 16:28:10 +0000 (UTC) Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by gabe.freedesktop.org (Postfix) with ESMTPS id 4A5156F596; Fri, 21 May 2021 16:28:09 +0000 (UTC) IronPort-SDR: wY/uoPdTN+FM4wS/blvlQbl8uW3Sv2xnAEKmlpgSZMgVixuyFY8uKXhKIXOWzNd1qT50nbF2qt qDpZ1TVwXvzg== X-IronPort-AV: E=McAfee;i="6200,9189,9991"; a="199578983" X-IronPort-AV: E=Sophos;i="5.82,319,1613462400"; d="scan'208";a="199578983" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 May 2021 09:28:08 -0700 IronPort-SDR: 10cd9HAvKgCkFheFimOlvOf/GDVGLTveUr7DrdJcIt91pk5USsUrpVQrQQYSzpkVbhd35aDkJx RY8yzP5xGj3A== X-IronPort-AV: E=Sophos;i="5.82,319,1613462400"; d="scan'208";a="475792196" Received: from unknown (HELO sdutt-i7) ([10.165.21.147]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 May 2021 09:28:08 -0700 Date: Fri, 21 May 2021 09:20:57 -0700 From: Matthew Brost To: Daniel Vetter Message-ID: <20210521162057.GB22003@sdutt-i7> References: <20210518235830.133834-1-matthew.brost@intel.com> <20210518235830.133834-3-matthew.brost@intel.com> <20210519171157.GA5202@sdutt-i7> <20210520151059.GA3416@sdutt-i7> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Subject: Re: [Intel-gfx] [RFC 2/2] drm/doc/rfc: i915 new parallel submission uAPI plan X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: intel-gfx , dri-devel , Jason Ekstrand , Mesa Dev , Daniel Vetter , karl@freedesktop.org, Christian =?iso-8859-1?Q?K=F6nig?= Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Thu, May 20, 2021 at 09:44:59PM +0200, Daniel Vetter wrote: > On Thu, May 20, 2021 at 08:10:59AM -0700, Matthew Brost wrote: > > On Thu, May 20, 2021 at 11:54:25AM +0200, Daniel Vetter wrote: > > > On Wed, May 19, 2021 at 7:19 PM Matthew Brost wrote: > > > > > > > > On Wed, May 19, 2021 at 01:10:04PM +0200, Daniel Vetter wrote: > > > > > On Tue, May 18, 2021 at 04:58:30PM -0700, Matthew Brost wrote: > > > > > > Add entry fpr i915 new parallel submission uAPI plan. > > > > > > > > > > > > v2: > > > > > > (Daniel Vetter): > > > > > > - Expand logical order explaination > > > > > > - Add dummy header > > > > > > - Only allow N BBs in execbuf IOCTL > > > > > > - Configure parallel submission per slot not per gem context > > > > > > > > > > > > Cc: Tvrtko Ursulin > > > > > > Cc: Tony Ye > > > > > > CC: Carl Zhang > > > > > > Cc: Daniel Vetter > > > > > > Cc: Jason Ekstrand > > > > > > Signed-off-by: Matthew Brost > > > > > > --- > > > > > > Documentation/gpu/rfc/i915_parallel_execbuf.h | 144 ++++++++++++++++++ > > > > > > Documentation/gpu/rfc/i915_scheduler.rst | 53 ++++++- > > > > > > 2 files changed, 196 insertions(+), 1 deletion(-) > > > > > > create mode 100644 Documentation/gpu/rfc/i915_parallel_execbuf.h > > > > > > > > > > > > diff --git a/Documentation/gpu/rfc/i915_parallel_execbuf.h b/Documentation/gpu/rfc/i915_parallel_execbuf.h > > > > > > new file mode 100644 > > > > > > index 000000000000..8c64b983ccad > > > > > > --- /dev/null > > > > > > +++ b/Documentation/gpu/rfc/i915_parallel_execbuf.h > > > > > > @@ -0,0 +1,144 @@ > > > > > > +#define I915_CONTEXT_ENGINES_EXT_PARALLEL_SUBMIT 2 /* see i915_context_engines_parallel_submit */ > > > > > > + > > > > > > +/* > > > > > > + * i915_context_engines_parallel_submit: > > > > > > + * > > > > > > + * Setup a slot to allow multiple BBs to be submitted in a single execbuf IOCTL. > > > > > > + * Those BBs will then be scheduled to run on the GPU in parallel. Multiple > > > > > > + * hardware contexts are created internally in the i915 run these BBs. Once a > > > > > > + * slot is configured for N BBs only N BBs can be submitted in each execbuf > > > > > > + * IOCTL and this is implict behavior (e.g. the user doesn't tell the execbuf > > > > > > + * IOCTL there are N BBs, the execbuf IOCTL know how many BBs there are based on > > > > > > + * the slots configuration). > > > > > > + * > > > > > > + * Their are two currently defined ways to control the placement of the > > > > > > + * hardware contexts on physical engines: default behavior (no flags) and > > > > > > + * I915_PARALLEL_IMPLICT_BONDS (a flag). More flags may be added the in the > > > > > > + * future as new hardware / use cases arise. Details of how to use this > > > > > > + * interface below above the flags. > > > > > > + * > > > > > > + * Returns -EINVAL if hardware context placement configuration invalid or if the > > > > > > + * placement configuration isn't supported on the platform / submission > > > > > > + * interface. > > > > > > + * Returns -ENODEV if extension isn't supported on the platform / submission > > > > > > + * inteface. > > > > > > + */ > > > > > > +struct i915_context_engines_parallel_submit { > > > > > > + struct i915_user_extension base; > > > > > > + > > > > > > + __u16 engine_index; /* slot for parallel engine */ > > > > > > + __u16 width; /* number of contexts per parallel engine */ > > > > > > + __u16 num_siblings; /* number of siblings per context */ > > > > > > + __u16 mbz16; > > > > > > > > > > Ok the big picture looks reasonable now, the flags still confuse me. > > > > > > > > > > > > > Yea, it is a bit confusing. > > > > > > > > > > +/* > > > > > > + * Default placement behvavior (currently unsupported): > > > > > > + * > > > > > > + * Rather than restricting parallel submission to a single class with a > > > > > > + * logically contiguous placement (I915_PARALLEL_IMPLICT_BONDS), add a mode that > > > > > > + * enables parallel submission across multiple engine classes. In this case each > > > > > > + * context's logical engine mask indicates where that context can placed. It is > > > > > > + * implied in this mode that all contexts have mutual exclusive placement (e.g. > > > > > > + * if one context is running CS0 no other contexts can run on CS0). > > > > > > + * > > > > > > + * Example 1 pseudo code: > > > > > > + * CSX[Y] = engine class X, logical instance Y > > > > > > + * INVALID = I915_ENGINE_CLASS_INVALID, I915_ENGINE_CLASS_INVALID_NONE > > > > > > + * set_engines(INVALID) > > > > > > + * set_parallel(engine_index=0, width=2, num_siblings=2, > > > > > > + * engines=CS0[0],CS0[1],CS1[0],CS1[1]) > > > > > > + * > > > > > > + * Results in the following valid placements: > > > > > > + * CS0[0], CS1[0] > > > > > > + * CS0[0], CS1[1] > > > > > > + * CS0[1], CS1[0] > > > > > > + * CS0[1], CS1[1] > > > > > > + * > > > > > > + * This can also be though of as 2 virtual engines: > > > > > > + * VE[0] = CS0[0], CS0[1] > > > > > > + * VE[1] = CS1[0], CS1[1] > > > > > > + * > > > > > > + * Example 2 pseudo code: > > > > > > + * CS[X] = generic engine of same class, logical instance X > > > > > > + * INVALID = I915_ENGINE_CLASS_INVALID, I915_ENGINE_CLASS_INVALID_NONE > > > > > > + * set_engines(INVALID) > > > > > > + * set_parallel(engine_index=0, width=2, num_siblings=3, > > > > > > + * engines=CS[0],CS[1],CS[2],CS[0],CS[1],CS[2]) > > > > > > + * > > > > > > + * Results in the following valid placements: > > > > > > + * CS[0], CS[1] > > > > > > + * CS[0], CS[2] > > > > > > + * CS[1], CS[0] > > > > > > + * CS[1], CS[2] > > > > > > + * CS[2], CS[0] > > > > > > + * CS[2], CS[1] > > > > > > + * > > > > > > + * > > > > > > + * This can also be though of as 2 virtual engines: > > > > > > + * VE[0] = CS[0], CS[1], CS[2] > > > > > > + * VE[1] = CS[0], CS[1], CS[2] > > > > > > + > > > > > > + * This enables a use case where all engines are created equally, we don't care > > > > > > + * where they are scheduled, we just want a certain number of resources, for > > > > > > + * those resources to be scheduled in parallel, and possibly across multiple > > > > > > + * engine classes. > > > > > > + */ > > > > > > > > > > So I don't really get what this does compared to setting the flag below. > > > > > Is this just about running the batchbuffers the wrong way round, i.e. if > > > > > you have (simplest case) > > > > > > > > > > width=2, num_sibglings=1, engines=CS[0], CS[1] > > > > > > > > > > Then both > > > > > CS[0], CS[1] > > > > > and > > > > > CS[1], CS[0] > > > > > are possible options for running 2 batches? Iow, the backend is allowed to > > > > > run the batchbuffers the wrong way round, which gains us nothing, since we > > > > > assume the batches take equally long and engines interchangeable. There is > > > > > no scheduling scenario where this additional flexibility can help. > > > > > > > > > > Also we don't have flags to select the only available and then specify an > > > > > entire pipe dream about what the non-flag mode does, without an > > > > > implementation. What is this about? > > > > > > > > > > If it's just "because bonded allowed this" then I think we should just > > > > > unceremonously ditch this. Bummer for the nice kerenldoc you wrote, but > > > > > welp. > > > > > > > > > > > > > High level the flags came out of internal discussions how this interface > > > > should look. The default placement behavior is theoretically possible > > > > with execlists but has no use cases. The GuC supports / current use > > > > cases are a subset of what is possible with I915_PARALLEL_IMPLICT_BONDS. > > > > > > > > Argued about for months and this is where we landed. At the end of the > > > > day I think we needed to show that this interface supports more > > > > placement rules than what the GuC supports / current use cases to future > > > > proof this interface. > > > > > > > > For what is it worth it seems kinda backwards that we landed on the > > > > default behavior not being supported in our current stack / HW. > > > > > > Yeah I think that should be inverted, doesn't make sense. > > > > > > What I still don't get (and I've read Tvrtko's reply with the example) > > > is what exactly is the difference between implicit and not implicit > > > mode? Can you do a single example where the only difference is whether > > > this flag is set, and then explain with that what are the actual > > > differences in scheduling options that the backend is allowed to pick > > > for the set of N patches? > > > > > > I'm feeling a bit dense, but I'm really not seeing what's even going on here :-( > > > > > > > > > + > > > > > > +/* > > > > > > + * I915_PARALLEL_IMPLICT_BONDS - Create implict bonds between each context. > > > > > > + * Each context must have the same number sibling and bonds are implictly create > > > > > > + * of the siblings. > > > > > > + * > > > > > > + * All of the below examples are in logical space. > > > > > > + * > > > > > > + * Example 1 pseudo code: > > > > > > + * CS[X] = generic engine of same class, logical instance X > > > > > > + * INVALID = I915_ENGINE_CLASS_INVALID, I915_ENGINE_CLASS_INVALID_NONE > > > > > > + * set_engines(INVALID) > > > > > > + * set_parallel(engine_index=0, width=2, num_siblings=1, > > > > > > + * engines=CS[0],CS[1], flags=I915_PARALLEL_IMPLICT_BONDS) > > > > > > + * > > > > > > + * Results in the following valid placements: > > > > > > + * CS[0], CS[1] > > > > > > + * > > > > > > + * Example 2 pseudo code: > > > > > > + * CS[X] = generic engine of same class, logical instance X > > > > > > + * INVALID = I915_ENGINE_CLASS_INVALID, I915_ENGINE_CLASS_INVALID_NONE > > > > > > + * set_engines(INVALID) > > > > > > + * set_parallel(engine_index=0, width=2, num_siblings=2, > > > > > > + * engines=CS[0],CS[2],CS[1],CS[3], flags=I915_PARALLEL_IMPLICT_BONDS) > > > > > > + * > > > > > > + * Results in the following valid placements: > > > > > > + * CS[0], CS[1] > > > > > > + * CS[2], CS[3] > > > > > > + * > > > > > > + * This can also be though of as 2 virtual engines: > > > > > > + * VE[0] = CS[0], CS[2] > > > > > > + * VE[1] = CS[1], CS[3] > > > > > > + * > > > > > > + * This enables a use case where all engines are not equal and certain placement > > > > > > + * rules are required (i.e. split-frame requires all contexts to be placed in a > > > > > > + * logically contiguous order on the VCS engines on gen11+ platforms). This use > > > > > > + * case (logically contiguous placement, within a single engine class) is > > > > > > + * supported when using GuC submission. Execlist mode could support all possible > > > > > > + * bonding configurations but currently doesn't support this extension. > > > > > > + */ > > > > > > +#define I915_PARALLEL_IMPLICT_BONDS (1<<0) > > > > > > > > > > Does this map to intel_context_set_nopreempt(), so we could implement it > > > > > also in execlist? > > > > > > > > > > > > > intel_context_set_nopreempt is preempt is part of how this would be > > > > implemented for execlists. For GuC submission there is a algorithm > > > > between the i915 and GuC that inserts same preemption points between > > > > each set of N batches. I believe the rules are if context 1 can > > > > preempted the rest of the contexts (2 - N) can safely be preempted. A go > > > > / join algorithm, implemented with semaphores, around the batches > > > > makes sure the i915 adheres to these rules. > > > > > > > > > Also is this just an artifact of the implementation, or is this somehow > > > > > required functionality for userspace, i.e. the workload fails if e.g. GuC > > > > > decides to preempt all LRC of a parallel virtual engine? Of course just > > > > > preempting one is a bit a bug (but execlist I think happily does that). > > > > > > > > > > > > > I think it is part of the implementation / HW limitations. Basically if > > > > N batches are running in parallel if one of the batches gets preempted > > > > it can hang all the other batches even if it gets restarted. Again the > > > > idea behind this is only preempt any of these contexts between each set > > > > of N batches. The GuC has no concept of batches only contexts hence the > > > > aforementioned algorithm to insert same preemption points between each > > > > set of batches. > > > > > > Well backend preempting one but not the other is a bug. I don't think > > > we need to talk about bugs :-) > > > > > > > I think it is more that backend can't preempt each context atomically as these > > are running on independent engines. Let say the backend tries to preempt 2 > > engines at the same time and only 1 responds, now we are broken with certain > > batches. With the algorithm implmented between the i915 and the Guc the GuC will > > try to preempt the first context if that works, all the other contexts can be > > preempted. > > Ah right, we might have a workload with long non-preemptible sections, but > I guess the MI_SEMAPHORE_WAIT can always preempt. So if GuC just tries on > one of these, it will result in tears. > > > > Now wrt a preempt mode in context creation, I think that makes sense. > > > I'm just wondering whether this is correct here in the parallel > > > submission (and why), or is it just an implementation artifact > > > (current backends are buggy if we'd allow them to preempt) or what's > > > going on. > > > > > > If this is just a case of "this is how current backends work, > > > userspace doesn't actually care whether we allow preempt or not" then > > > I think we should just document the behavior and that's it. Adding > > > uapi for an option for which there's not even an implementation isn't > > > great. > > > > > > > I don't think it is a case of 'this is how current backends work...', I think > > user space knows if it is ok for 1 of the batches to preempted and not the > > others without breaking the batches. > > Yeah this makes more sense as an explanation: Currently the backend (guc > or execlist) figure out whether something can be preempted by just trying. > Since we're dealing with N contexts that's a suboptimal approach, and we > need a flag that indicates whether it's worth it or not. > > So makes sense to me to have this. I guess userspace does actually need > both modes for now, depending upon what it's doing? > -Daniel I agree that is makes sense to have - an explict flag saying it isn't safe to preempt one of the N batches by itself or letting the driver do whatever it wants regarding preemption. The current use case is it can't preempt a single batch but it may change going forward. Lastly, there is overhead to non-preempt mid batch feature so being able to turn it off seems reasonable to me. Matt > > > > > Matt > > > > > But if we can actually choose, and userspace wants to, then I'm all > > > fine with this. And we can always move this to a more generic place if > > > other engines need preempt control later on too. > > > > > > Cheers, Daniel > > > > > > > > > > Matt > > > > > > > > > Cheers, Daniel > > > > > > > > > > > +/* > > > > > > + * Do not allow BBs to be preempted mid BB rather insert coordinated preemption > > > > > > + * points on all hardware contexts between each set of BBs. An example use case > > > > > > + * of this feature is split-frame on gen11+ hardware. When using this feature a > > > > > > + * BB must be submitted on each hardware context in the parallel gem context. > > > > > > + * The execbuf2 IOCTL enforces the user adheres to policy. > > > > > > + */ > > > > > > +#define I915_PARALLEL_NO_PREEMPT_MID_BATCH (1<<1) > > > > > > +#define __I915_PARALLEL_UNKNOWN_FLAGS (-(I915_PARALLEL_NO_PREEMPT_MID_BATCH << 1)) > > > > > > + __u64 flags; /* all undefined flags must be zero */ > > > > > > + __u64 mbz64[3]; /* reserved for future use; must be zero */ > > > > > > + > > > > > > + /* > > > > > > + * width (i) * num_siblings (j) in length > > > > > > + * index = j + i * num_siblings > > > > > > + */ > > > > > > + struct i915_engine_class_instance engines[0]; > > > > > > +} __attribute__ ((packed)); > > > > > > + > > > > > > diff --git a/Documentation/gpu/rfc/i915_scheduler.rst b/Documentation/gpu/rfc/i915_scheduler.rst > > > > > > index 7faa46cde088..64c539486ee4 100644 > > > > > > --- a/Documentation/gpu/rfc/i915_scheduler.rst > > > > > > +++ b/Documentation/gpu/rfc/i915_scheduler.rst > > > > > > @@ -82,4 +82,55 @@ https://spec.oneapi.com/level-zero/latest/core/api.html#ze-command-queue-priorit > > > > > > > > > > > > New parallel submission uAPI > > > > > > ============================ > > > > > > -Details to come in a following patch. > > > > > > +The existing bonding uAPI is completely broken with GuC submission because > > > > > > +whether a submission is a single context submit or parallel submit isn't known > > > > > > +until execbuf time activated via the I915_SUBMIT_FENCE. To submit multiple > > > > > > +contexts in parallel with the GuC the context must be explictly registered with > > > > > > +N contexts and all N contexts must be submitted in a single command to the GuC. > > > > > > +These interfaces doesn't support dynamically changing between N contexts as the > > > > > > +bonding uAPI does. Hence the need for a new parallel submission interface. Also > > > > > > +the legacy bonding uAPI is quite confusing and not intuitive at all. > > > > > > + > > > > > > +The new parallel submission uAPI consists of 3 parts: > > > > > > + > > > > > > +* Export engines logical mapping > > > > > > +* A 'set_parallel' extension to configure contexts for parallel > > > > > > + submission > > > > > > +* Extend execbuf2 IOCTL to support submitting N BBs in a single IOCTL > > > > > > + > > > > > > +Export engines logical mapping > > > > > > +------------------------------ > > > > > > +Certain use cases require BBs to be placed on engine instances in logical order > > > > > > +(e.g. split-frame on gen11+). The logical mapping of engine instances can change > > > > > > +based on fusing. Rather than making UMDs be aware of fusing, simply expose the > > > > > > +logical mapping with the existing query engine info IOCTL. Also the GuC > > > > > > +submission interface currently only supports submitting multiple contexts to > > > > > > +engines in logical order which is a new requirement compared to execlists. > > > > > > +Lastly, all current platforms have at most 2 instances and the logical order is > > > > > > +the same a uABI order. This will change on platforms with more than 2 instances. > > > > > > + > > > > > > +A single bit will be added to drm_i915_engine_info.flags indicating that the > > > > > > +logical instance has been returned and a new field, > > > > > > +drm_i915_engine_info.logical_instance, returns the logical instance. > > > > > > + > > > > > > +A 'set_parallel' extension to configure contexts for parallel submission > > > > > > +------------------------------------------------------------------------ > > > > > > +The 'set_parallel' extension configures a slot for parallel submission of N BBs. > > > > > > +It is setup step that should be called before using any of the contexts. See > > > > > > +I915_CONTEXT_ENGINES_EXT_LOAD_BALANCE or I915_CONTEXT_ENGINES_EXT_BOND for > > > > > > +similar existing examples. Once a slot is configured for parallel submission the > > > > > > +execbuf2 IOCTL can be called submiting N BBs in a single IOCTL. Initially only > > > > > > +support GuC submission. Execlist support can be added later if needed. > > > > > > + > > > > > > +Add I915_CONTEXT_ENGINES_EXT_PARALLEL_SUBMIT and > > > > > > +i915_context_engines_parallel_submit to the uAPI to implement this extension. > > > > > > + > > > > > > +Extend execbuf2 IOCTL to support submitting N BBs in a single IOCTL > > > > > > +------------------------------------------------------------------- > > > > > > +Contexts that have been configured with the 'set_parallel' extension are allowed > > > > > > +to submit N BBs in a single execbuf2 IOCTL. The BBs are either the last N > > > > > > +objects in the drm_i915_gem_exec_object2 list or the first N if > > > > > > +I915_EXEC_BATCH_FIRST is set. The number of BBs is implict based on the slot > > > > > > +submitted and how it has been configured by 'set_parallel' or other extensions. > > > > > > +No uAPI changes in the execbuf IOCTL but worth mentioning the new behavior of > > > > > > +the IOCTL. > > > > > > -- > > > > > > 2.28.0 > > > > > > > > > > > > _______________________________________________ > > > > > > Intel-gfx mailing list > > > > > > Intel-gfx@lists.freedesktop.org > > > > > > https://lists.freedesktop.org/mailman/listinfo/intel-gfx > > > > > > > > > > -- > > > > > Daniel Vetter > > > > > Software Engineer, Intel Corporation > > > > > http://blog.ffwll.ch > > > > > > > > > > > > -- > > > Daniel Vetter > > > Software Engineer, Intel Corporation > > > http://blog.ffwll.ch > > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx