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 6405BC433EF for ; Mon, 7 Feb 2022 13:36:31 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id CA38E10E2EC; Mon, 7 Feb 2022 13:36:30 +0000 (UTC) Received: from mga06.intel.com (mga06.intel.com [134.134.136.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id 9B94E10E2EC for ; Mon, 7 Feb 2022 13:36:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1644240988; x=1675776988; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=Cl41drjRXEIn2zBuDXJ6Mzhwe9xrs4u/wQBhwxGG/JU=; b=A8ZbkC/9YLTqYNQ1rTIb8eIEdZ9M6YbCB8EqlKJVxpEJpDazUg20OMnq xcTDnWWVlElNlYBD2J4eJWkLa+Os+Lihi2DH9nZEqJnOyOWs2ZOZSQ+fJ nHiKKHaMbZnsy4vgLDnz/QXL0vvuedQmFRcI69uIBh2Nf4LPymwuOpPBI 1S4tdg5Lm6NjE2/e2dv325UDUshRFOpFk/KxVzmNDvwpHOljUtpNbPTBY bD9QLAbRZQ1HR6QLv3LZ2Y86FKPeVn/XgYJ61LqFdHJJ0/Rd1SyvIAgMu zJpBggMFiN8tNlqIyJFDRWB2yYu8mXTgpPWvfTMezp6KayCwiBIhl1tb3 Q==; X-IronPort-AV: E=McAfee;i="6200,9189,10250"; a="309457605" X-IronPort-AV: E=Sophos;i="5.88,349,1635231600"; d="scan'208";a="309457605" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Feb 2022 05:36:27 -0800 X-IronPort-AV: E=Sophos;i="5.88,349,1635231600"; d="scan'208";a="481584418" Received: from conroyco-mobl2.ger.corp.intel.com (HELO [10.213.251.21]) ([10.213.251.21]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Feb 2022 05:36:25 -0800 Message-ID: <78a464bd-a591-ac9b-51ca-b4f227d42ada@linux.intel.com> Date: Mon, 7 Feb 2022 13:36:23 +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: =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= References: <20220204012210.1517091-1-vivek.kasireddy@intel.com> <4475de33-22b3-edbb-2995-f72e9bcc4162@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 2/2] drm/i915/gem: Don't try to map and fence large scanout buffers (v6) 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 Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 07/02/2022 13:24, Ville Syrjälä wrote: > On Mon, Feb 07, 2022 at 11:47:16AM +0000, Tvrtko Ursulin wrote: >> >> On 07/02/2022 10:58, Ville Syrjälä wrote: >>> On Thu, Feb 03, 2022 at 05:22:10PM -0800, 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. >>>> >>>> Cc: Ville Syrjälä >>>> Cc: Maarten Lankhorst >>>> Cc: Tvrtko Ursulin >>>> Cc: Manasi Navare >>>> Signed-off-by: Vivek Kasireddy >>>> --- >>>> drivers/gpu/drm/i915/i915_gem.c | 120 ++++++++++++++++++++++++-------- >>>> 1 file changed, 90 insertions(+), 30 deletions(-) >>>> >>>> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c >>>> index e3a2c2a0e156..39f0d17550c3 100644 >>>> --- a/drivers/gpu/drm/i915/i915_gem.c >>>> +++ b/drivers/gpu/drm/i915/i915_gem.c >>>> @@ -46,6 +46,7 @@ >>>> #include "gem/i915_gem_mman.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" >>>> @@ -876,6 +877,92 @@ 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) >>>> +{ >>>> + struct drm_i915_private *i915 = to_i915(obj->base.dev); >>>> + struct i915_ggtt *ggtt = to_gt(i915)->ggtt; >>>> + struct drm_mm_node *hole; >>>> + u64 hole_start, hole_end, start, end; >>>> + u64 fence_size, fence_alignment; >>>> + unsigned int count = 0; >>>> + >>>> + /* >>>> + * If the required space is larger than the available >>>> + * aperture, we will not able to find a slot for the >>>> + * object and unbinding the object now will be in >>>> + * vain. Worse, doing so may cause us to ping-pong >>>> + * the object in and out of the Global GTT and >>>> + * waste a lot of cycles under the mutex. >>>> + */ >>>> + if (obj->base.size > ggtt->mappable_end) >>>> + return -E2BIG; >>>> + >>>> + /* >>>> + * If NONBLOCK is set the caller is optimistically >>>> + * trying to cache the full object within the mappable >>>> + * aperture, and *must* have a fallback in place for >>>> + * situations where we cannot bind the object. We >>>> + * can be a little more lax here and use the fallback >>>> + * more often to avoid costly migrations of ourselves >>>> + * and other objects within the aperture. >>>> + */ >>>> + if (!(flags & PIN_NONBLOCK)) >>>> + return 0; >>>> + >>>> + /* >>>> + * We only consider objects whose size is at-least a quarter of >>>> + * the aperture to be too big and subject them to the new >>>> + * heuristic below. >>>> + */ >>>> + if (obj->base.size < ggtt->mappable_end / 4) >>>> + return 0; >>> >>> That seems a fairly arbitrary thing to put here. Maybe something the >>> caller should check/specify? >> >> I have no strong opinion on this one. In my mind I categorised it under >> "is it a large framebuffer" heuristics. Previously it was less than one >> half of aperture always okay, now one quarter, plus 2x hole check if >> larger. Both are heuristics. I even mentioned earlier if 2x should be an >> input parameter as well, but again, given it's not an exported function >> couldn't really justify it. > > Is there any point in even having this extra check? If we > don't think checking this is worth the hassle then why call > the function at all? The "/4" one? It was my suggestion to avoid the hole search if we can know based on size it cannot be a frame buffer that would be affected by the ping-ping problem. Granted that was before the rbtree hole search, when it was traversing the un-ordered linked list of holes. What is the correct size threshold I don't know. >>>> + >>>> + if (HAS_GMCH(i915) || DISPLAY_VER(i915) < 11 || >>>> + !i915_gem_object_is_framebuffer(obj)) >>>> + return 0; >>> >>> None of that seems appropriate for a generic gem function >>> with this name. >> >> It's not exported though, maybe remove i915_gem prefix to avoid any >> ideas of it being generic? > > These checks don't even seem to doing anything useful. HAS_GMCH should > already be covered by always setting PIN_MAPPABLE and hence O_NONBLOCK > is never even tried, the pre-icl vs. icl+ check should not exist at all > IMO, and if this is only called for framebuffers then why does the code > pretend that is not the case? > > So I would suggest just ditching all these checks, and then the function > even does what it says on the tin. Change log for v3 made me think at least some of this was your suggestion so I did not think about it further. :) No strong opinion either. Regards, Tvrtko