** Summary changed:
- Request backport of two i915/Intel Arc GPU patches
+ i915: Fixup regressions introduced with enabling single CCS engine
** Changed in: linux (Ubuntu Noble)
Status: New => In Progress
** Changed in: linux (Ubuntu Noble)
Importance: Undecided => Medium
** Changed in: linux (Ubuntu Noble)
Assignee: (unassigned) => Matthew Ruffell (mruffell)
** Description changed:
- Hello Ubuntu Linux Kernel Team,
+ BugLink: https://bugs.launchpad.net/bugs/2072755
- Recently, Ubuntu 24.04 bumped the kernel version to linux 6.8.8
- (6.8.0-38.38 pkg version), which introduced an i915 regression affecting
- GPU accelerated video transcoding on Intel Arc GPU. This bug affects all
- linux 6.8.5+ kernels and was not fully fixed until linux 6.9.4.
+ [Impact]
- https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2068087
+ 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.
- The issue makes the ffmpeg command fail and throws i915 error in dmesg.
- `[ 81.026591] Fence expiration time out i915-0000:01:00.0:ffmpeg[521]:2!`
+ This all happened in:
+ commit 6db31251bb265813994bfb104eb4b4d0f44d64fb
+ Author: Andi Shyti <andi.sh...@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.sh...@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.sh...@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@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
-
- Could you please backport these two patches to the Ubuntu kernel branch
- to fix the regression?
-
- https://gitlab.com/linux-
- kernel/stable/-/commit/fdf6c286478698ed901db1bd5a8702667f796c28
-
- https://gitlab.com/linux-
- kernel/stable/-/commit/e9250578ac6278dfd24a57c326eb805b3bdb0e31
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https://bugs.launchpad.net/bugs/2072755
Title:
i915: Fixup regressions introduced with enabling single CCS engine
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