ACK/Cmnt: [SRU][Noble][PATCH 0/1] i915: Fixup regressions introduced with enabling single CCS engine

Mon Jul 15 12:27:28 UTC 2024

On Mon, Jul 15, 2024 at 02:45:32PM +1200, Matthew Ruffell wrote:
> BugLink: https://bugs.launchpad.net/bugs/2072755
> 
> [Impact]
> 
> Recently, the Intel i915 susbsystem underwent a change that limited the number
> of CCS engines that were initialised by default, and exposed to the user.
> Different chipsets have differing amounts of CCS engines, but most available in
> the market have 4 CCS engines. The new change just starts a single engine only,
> and allocates all CCS slices to this single engine. This single engine is then
> exposed to userspace. This effort is to workaround a hardware bug.
> 
> This all happened in:
> 
> commit 6db31251bb265813994bfb104eb4b4d0f44d64fb
> Author: Andi Shyti <andi.shyti at linux.intel.com>
> Date:   Thu Mar 28 08:34:05 2024 +0100
> Subject: drm/i915/gt: Enable only one CCS for compute workload
> Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6db31251bb265813994bfb104eb4b4d0f44d64fb
> 
> which landed in:
> 
> $ git describe --contains 67f164e8510b16bda18642464863dba87a33d8cb
> Ubuntu-6.8.0-38.38~525
> 
> There have been some side effects as a result of these changes, leading to
> failure of userspace applications, namely in video transcoding with ffmepg,
> resulting in fence expiration errors in dmesg like:
> 
> [ 81.026591] Fence expiration time out i915-0000:01:00.0:ffmpeg[521]:2!
> 
> There has also been a performance impact introduced by this change, which
> dropped performance of the GPU to 1/4 of what it was previously. This is likely
> due to most ARC GPUs usually having 4 CCS engines, and going down to 1 only
> without actually allocating the other three. 
> 
> There are no workarounds. Users are suggested to downgrade to 6.8.0-36-generic
> while the fix is coming.
> 
> [Fix]
> 
> The regression was fixed by these two commits:
> 
> commit aee54e282002a127612b71255bbe879ec0103afd
> Author: Andi Shyti <andi.shyti at linux.intel.com>
> Date: Fri Apr 26 02:07:23 2024 +0200
> Subject: drm/i915/gt: Automate CCS Mode setting during engine resets
> Link: https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/noble/commit/?id=aee54e282002a127612b71255bbe879ec0103afd
> 
> commit ee01b6a386eaf9984b58a2476e8f531149679da9
> Author: Andi Shyti <andi.shyti at linux.intel.com>
> Date: Fri May 17 11:06:16 2024 +0200
> Subject: drm/i915/gt: Fix CCS id's calculation for CCS mode setting
> Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ee01b6a386eaf9984b58a2476e8f531149679da9
> 
> "drm/i915/gt: Automate CCS Mode setting during engine resets" is already applied
> to noble/master-next through upstream stable v6.8.10.
> 
> We just need "drm/i915/gt: Fix CCS id's calculation for CCS mode setting". It is
> queued up for v6.9.4, but that could still be another SRU cycle or two away. So
> send it now.
> 
> "drm/i915/gt: Fix CCS id's calculation for CCS mode setting" restores another
> 1/4 performance, but some performance issues still remain, and will hopefully
> be addressed in a future patch.
> 
> [Testcase]
> 
> This affects video transcoding with ffmpeg, on machines equipped with Intel ARC
> GPUs.
> 
> An example ffmpeg command might be:
> 
> /usr/lib/jellyfin-ffmpeg/ffmpeg -analyzeduration 200M -probesize 1G -ss 00:00:03.000 -noaccurate_seek -init_hw_device vaapi=va:,kernel_driver=i915,driver=iHD -init_hw_device qsv=qs at va -filter_hw_device qs -hwaccel vaapi -hwaccel_output_format vaapi -noautorotate -i file:"/path/to/1080_video.mkv" -noautoscale -map_metadata -1 -map_chapters -1 -threads 0 -map 0:0 -map 0:1 -map -0:s -codec:v:0 av1_qsv -preset veryfast -b:v 3616000 -maxrate 3616000 -bufsize 7232000 -g:v:0 72 -keyint_min:v:0 72 -vf "setparams=color_primaries=bt709:color_trc=bt709:colorspace=bt709,scale_vaapi=w=1280:h=720:format=nv12:extra_hw_frames=24,hwmap=derive_device=qsv,format=qsv" -codec:a:0 libfdk_aac -ac 2 -vbr:a 5 -copyts -avoid_negative_ts disabled -max_muxing_queue_size 2048 -f hls -max_delay 5000000 -hls_time 3 -hls_segment_type fmp4 -hls_fmp4_init_filename "c30716eb121448346fcc00a2440071a3-1.mp4" -start_number 1 -hls_segment_filename "/var/lib/jellyfin/transcodes/c30716eb121448346fcc00a2440071a3%d.mp4" -hls_playlist_type vod -hls_list_size 0 -y "/var/lib/jellyfin/transcodes/c30716eb121448346fcc00a2440071a3.m3u8
> 
> Another user on bug 2072933 came up with this minimalist reproducer:
> 
> #include <cstdio>
> #include <sycl/sycl.hpp>
> 
> int main() {
>   // auto selector = sycl::cpu_selector_v; // Works fine
>   auto selector = sycl::gpu_selector_v;
> 
>   auto queue = sycl::queue(selector);
> 
>   printf("Hello\n");
>   queue.submit([&](sycl::handler &cgh) {
>     cgh.parallel_for(sycl::range(1), [=](sycl::item<1> item) {});
>   });
>   queue.wait();
>   printf("Bye\n");
> 
>   return 0;
> }
> 
> $ icpx -fsycl sycltest.cpp -o sycltest
> $ ./sycltest
> 
> These commands should run successfully to completion. On failure, they will
> emit in dmesg:
> 
> [ 81.026591] Fence expiration time out i915-0000:01:00.0:ffmpeg[521]:2!
> 
> A test kernel is available in the following ppa:
> 
> https://launchpad.net/~mruffell/+archive/ubuntu/lp2072755-test
> 
> If you install the test kernel, things should work correctly.
> 
> [Where problems could occur]
> 
> This issue affects users of i915, which is a pretty universal integrated GPU
> present on Intel processors. While these patches are unlikely to cause outages
> that stop the primary display from functioning, any further regressions may add
> additional performance impact or prevent workloads from executing correctly.
> 
> These patches are all accepted into upstream -stable, and we would consume them
> in due course anyway.
> 
> If a regression were to occur, there are no workarounds, and users would need to
> select an older kernel until a fix is available.
> 
> [Other info]
> 
> Upstream Bug:
> https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/10895
> 
> Andi Shyti (1):
>   drm/i915/gt: Fix CCS id's calculation for CCS mode setting
> 
>  drivers/gpu/drm/i915/gt/intel_engine_cs.c   | 6 ++++++
>  drivers/gpu/drm/i915/gt/intel_gt_ccs_mode.c | 2 +-
>  drivers/gpu/drm/i915/gt/intel_gt_types.h    | 8 ++++++++
>  3 files changed, 15 insertions(+), 1 deletion(-)
> 
> -- 
> 2.45.2
> 
> 
> -- 
> kernel-team mailing list
> kernel-team at lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team

An upstream stable update for noble that is based off of v6.9.4 is being
prepared at the moment and should land in the next SRU cycle. So
depending on the order of which either the update or this patch
submission will be applied, one will be dropped.

Acked-by: Manuel Diewald <manuel.diewald at canonical.com>

-- 
 Manuel
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