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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 5470CC433F5 for ; Tue, 15 Mar 2022 09:45:30 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 07D9310E985; Tue, 15 Mar 2022 09:45:27 +0000 (UTC) Received: from mga06.intel.com (mga06.intel.com [134.134.136.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id 3A07310E975; Tue, 15 Mar 2022 09:45:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1647337525; x=1678873525; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=eyfZyUrDHyhMxReq/zn0CQTHs/y5Xwqz/T+Ytfth6R8=; b=N9710aZ8SWQxXdM0GucbvHIBv/8eq7WT9vlJtmWhH/8q8RdQaOI7oLE+ oqvorsNWvrWl9IFpi0v2plBYOI7R5/SxDTyPUFITBD/ACuks/mVQqz3Um iF/KPKbQNdDKR0UAQyQbjUtI8NrVX3rOhkP/j+h5psOIgGRs4yC55YP+F r4nP15qDRxe2qRn7djfx3Jxn1LWeg17Mr5FXh2qZ1qxS+LRIoYvu05sf3 jNAqL0N7AvmtYxfQfxepPyPCNkyTPQEe/CpsNBhQ7FiNzqevJvPa6ZX6D i2usFcr+NMWLG/aWsMH44SA/1vGbzgLWQ/cFNFhZ0tzm0kuwOpzkgdYJn w==; X-IronPort-AV: E=McAfee;i="6200,9189,10286"; a="316979709" X-IronPort-AV: E=Sophos;i="5.90,182,1643702400"; d="scan'208";a="316979709" Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Mar 2022 02:45:24 -0700 X-IronPort-AV: E=Sophos;i="5.90,182,1643702400"; d="scan'208";a="549539526" Received: from rdoostne-mobl.amr.corp.intel.com (HELO [10.212.38.21]) ([10.212.38.21]) by fmsmga007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Mar 2022 02:45:23 -0700 Message-ID: Date: Tue, 15 Mar 2022 09:45:20 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Content-Language: en-US To: "Kasireddy, Vivek" , Daniel Vetter References: <20220307202121.389550-1-vivek.kasireddy@intel.com> <20220307202121.389550-3-vivek.kasireddy@intel.com> <1f9db89a-0d31-d9f5-2b4d-7856aa9ffa01@linux.intel.com> From: Tvrtko Ursulin Organization: Intel Corporation UK Plc In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Subject: Re: [Intel-gfx] [PATCH v6 2/2] drm/i915/gem: Don't try to map and fence large scanout buffers (v9) 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@lists.freedesktop.org" , "dri-devel@lists.freedesktop.org" Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 15/03/2022 07:28, Kasireddy, Vivek wrote: > Hi Tvrtko, Daniel, > >> >> On 11/03/2022 09:39, Daniel Vetter wrote: >>> On Mon, 7 Mar 2022 at 21:38, Vivek Kasireddy wrote: >>>> >>>> On platforms capable of allowing 8K (7680 x 4320) modes, pinning 2 or >>>> more framebuffers/scanout buffers results in only one that is mappable/ >>>> fenceable. Therefore, pageflipping between these 2 FBs where only one >>>> is mappable/fenceable creates latencies large enough to miss alternate >>>> vblanks thereby producing less optimal framerate. >>>> >>>> This mainly happens because when i915_gem_object_pin_to_display_plane() >>>> is called to pin one of the FB objs, the associated vma is identified >>>> as misplaced and therefore i915_vma_unbind() is called which unbinds and >>>> evicts it. This misplaced vma gets subseqently pinned only when >>>> i915_gem_object_ggtt_pin_ww() is called without PIN_MAPPABLE. This >>>> results in a latency of ~10ms and happens every other vblank/repaint cycle. >>>> Therefore, to fix this issue, we try to see if there is space to map >>>> at-least two objects of a given size and return early if there isn't. This >>>> would ensure that we do not try with PIN_MAPPABLE for any objects that >>>> are too big to map thereby preventing unncessary unbind. >>>> >>>> Testcase: >>>> Running Weston and weston-simple-egl on an Alderlake_S (ADLS) platform >>>> with a 8K@60 mode results in only ~40 FPS. Since upstream Weston submits >>>> a frame ~7ms before the next vblank, the latencies seen between atomic >>>> commit and flip event are 7, 24 (7 + 16.66), 7, 24..... suggesting that >>>> it misses the vblank every other frame. >>>> >>>> Here is the ftrace snippet that shows the source of the ~10ms latency: >>>> i915_gem_object_pin_to_display_plane() { >>>> 0.102 us | i915_gem_object_set_cache_level(); >>>> i915_gem_object_ggtt_pin_ww() { >>>> 0.390 us | i915_vma_instance(); >>>> 0.178 us | i915_vma_misplaced(); >>>> i915_vma_unbind() { >>>> __i915_active_wait() { >>>> 0.082 us | i915_active_acquire_if_busy(); >>>> 0.475 us | } >>>> intel_runtime_pm_get() { >>>> 0.087 us | intel_runtime_pm_acquire(); >>>> 0.259 us | } >>>> __i915_active_wait() { >>>> 0.085 us | i915_active_acquire_if_busy(); >>>> 0.240 us | } >>>> __i915_vma_evict() { >>>> ggtt_unbind_vma() { >>>> gen8_ggtt_clear_range() { >>>> 10507.255 us | } >>>> 10507.689 us | } >>>> 10508.516 us | } >>>> >>>> v2: Instead of using bigjoiner checks, determine whether a scanout >>>> buffer is too big by checking to see if it is possible to map >>>> two of them into the ggtt. >>>> >>>> v3 (Ville): >>>> - Count how many fb objects can be fit into the available holes >>>> instead of checking for a hole twice the object size. >>>> - Take alignment constraints into account. >>>> - Limit this large scanout buffer check to >= Gen 11 platforms. >>>> >>>> v4: >>>> - Remove existing heuristic that checks just for size. (Ville) >>>> - Return early if we find space to map at-least two objects. (Tvrtko) >>>> - Slightly update the commit message. >>>> >>>> v5: (Tvrtko) >>>> - Rename the function to indicate that the object may be too big to >>>> map into the aperture. >>>> - Account for guard pages while calculating the total size required >>>> for the object. >>>> - Do not subject all objects to the heuristic check and instead >>>> consider objects only of a certain size. >>>> - Do the hole walk using the rbtree. >>>> - Preserve the existing PIN_NONBLOCK logic. >>>> - Drop the PIN_MAPPABLE check while pinning the VMA. >>>> >>>> v6: (Tvrtko) >>>> - Return 0 on success and the specific error code on failure to >>>> preserve the existing behavior. >>>> >>>> v7: (Ville) >>>> - Drop the HAS_GMCH(i915), DISPLAY_VER(i915) < 11 and >>>> size < ggtt->mappable_end / 4 checks. >>>> - Drop the redundant check that is based on previous heuristic. >>>> >>>> v8: >>>> - Make sure that we are holding the mutex associated with ggtt vm >>>> as we traverse the hole nodes. >>>> >>>> v9: (Tvrtko) >>>> - Use mutex_lock_interruptible_nested() instead of mutex_lock(). >>>> >>>> Cc: Ville Syrjälä >>>> Cc: Maarten Lankhorst >>>> Cc: Tvrtko Ursulin >>>> Cc: Manasi Navare >>>> Reviewed-by: Tvrtko Ursulin >>>> Signed-off-by: Vivek Kasireddy >>>> --- >>>> drivers/gpu/drm/i915/i915_gem.c | 128 +++++++++++++++++++++++--------- >>>> 1 file changed, 94 insertions(+), 34 deletions(-) >>>> >>>> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c >>>> index 9747924cc57b..e0d731b3f215 100644 >>>> --- a/drivers/gpu/drm/i915/i915_gem.c >>>> +++ b/drivers/gpu/drm/i915/i915_gem.c >>>> @@ -49,6 +49,7 @@ >>>> #include "gem/i915_gem_pm.h" >>>> #include "gem/i915_gem_region.h" >>>> #include "gem/i915_gem_userptr.h" >>>> +#include "gem/i915_gem_tiling.h" >>>> #include "gt/intel_engine_user.h" >>>> #include "gt/intel_gt.h" >>>> #include "gt/intel_gt_pm.h" >>>> @@ -882,6 +883,96 @@ static void discard_ggtt_vma(struct i915_vma *vma) >>>> spin_unlock(&obj->vma.lock); >>>> } >>>> >>>> +static int >>>> +i915_gem_object_fits_in_aperture(struct drm_i915_gem_object *obj, >>>> + u64 alignment, u64 flags) >>> >>> Tvrtko asked me to ack the first patch, but then I looked at this and >>> started wondering. >>> >>> Conceptually this doesn't pass the smell test. What if we have >>> multiple per-crtc buffers? Multiple planes on the same crtc? What if >>> the app does triple buffer? You'll be forever busy tuning this >>> heuristics, which can't fundamentally be fixed I think. The old "half >>> of mappable" heuristic isn't really better, but at least it was dead >>> simple. >>> >>> Imo what we need here is a change in approach: >>> 1. Check whether the useable view for scanout exists already. If yes, >>> use that. This should avoid the constant unbinding stalls. >>> 2. Try to in buffer to mappabley, but without evicting anything (so >>> not the non-blocking thing) >>> 3. Pin the buffer with the most lenient approach >>> >>> Even the non-blocking interim stage is dangerous, since it'll just >>> result in other buffers (e.g. when triple-buffering) getting unbound >>> and we're back to the same stall. Note that this could have an impact >>> on cpu rendering compositors, where we might end up relying a lot more >>> partial views. But as long as we are a tad more aggressive (i.e. the >>> non-blocking binding) in the mmap path that should work out to keep >>> everything balanced, since usually you render first before you display >>> anything. And so the buffer should end up in the ideal place. >>> >>> I'd try to first skip the 2. step since I think it'll require a bit of >>> work, and frankly I don't think we care about the potential fallout. >> >> To be sure I understand, you propose to stop trying to pin mappable by default. Ie. stop >> respecting this comment from i915_gem_object_pin_to_display_plane: >> >> /* >> * As the user may map the buffer once pinned in the display plane >> * (e.g. libkms for the bootup splash), we have to ensure that we >> * always use map_and_fenceable for all scanout buffers. However, >> * it may simply be too big to fit into mappable, in which case >> * put it anyway and hope that userspace can cope (but always first >> * try to preserve the existing ABI). >> */ > [Kasireddy, Vivek] Digging further, this is what the commit message that added > the above comment says: > commit 2efb813d5388e18255c54afac77bd91acd586908 > Author: Chris Wilson > Date: Thu Aug 18 17:17:06 2016 +0100 > > drm/i915: Fallback to using unmappable memory for scanout > > The existing ABI says that scanouts are pinned into the mappable region > so that legacy clients (e.g. old Xorg or plymouthd) can write directly > into the scanout through a GTT mapping. However if the surface does not > fit into the mappable region, we are better off just trying to fit it > anywhere and hoping for the best. (Any userspace that is capable of > using ginormous scanouts is also likely not to rely on pure GTT > updates.) With the partial vma fault support, we are no longer > restricted to only using scanouts that we can pin (though it is still > preferred for performance reasons and for powersaving features like > FBC). > >> >> By a quick look, for this case it appears we would end up creating partial views for CPU >> access (since the normal mapping would be busy/unpinnable). Worst case for this is to >> create a bunch of 1MiB VMAs so something to check would be how long those persist in >> memory before they get released. Or perhaps the bootup splash use case is not common >> these days? > [Kasireddy, Vivek] AFAIK, Plymouth is still the default bootup splash service on Fedora, > Ubuntu and most other distributions. And, I took a quick look at it and IIUC, it (Plymouth's > drm plugin) seems to create a dumb FB, mmap and update it via the dirty_fb ioctl. This > would not to be a problem on ADL-S where there is space in mappable for one 8K FB. > FBC is a good point - correct me if I am wrong, but if we dropped trying to map in aperture by default it looks like we would lose it and that would be a significant power regression. In which case it doesn't seem like that would be an option. Which I think leaves us with _some_ heuristics in any case. 1) N-holes heuristics. 2) Don't ever try PIN_MAPPABLE for framebuffers larger than some percentage of aperture. Could this solve the 8k issue, most of the time, maybe? Could the current "aperture / 2" test be expressed generically in some terms? Like "(aperture - 10% (or some absolute value)) / 2" to account for non-fb objects? I forgot what you said the relationship between aperture size and 8k fb size was. 3) Don't evict for PIN_MAPPABLE mismatches when i915_gem_object_ggtt_pin_ww->i915_vma_misplaced is called on behalf of i915_gem_object_pin_to_display_plane. Assumption being if we ended up with a non-mappable fb to start with, we must not try to re-bind it or we risk ping-pong latencies. The last would I guess need to distinguish between PIN_MAPPABLE passed in versus opportunistically added by i915_gem_object_pin_to_display_plane. How intrusive would it be to implement this option I am not sure without trying myself. > Given this, do you think it would work if we just preserve the existing behavior and > tweak the heuristic introduced in this patch to look for space in aperture for only > one FB instead of two? Or, is there no good option for solving this issue other than > to create 1MB VMAs? I did not get how having one hole would solve the issue. Wouldn't it still hit the re-bind ping-pong? Or there isn't even a single hole for 8k fb typically? Regards, Tvrtko