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

Mon Jul 15 04:03:02 UTC 2024

On Mon, Jul 15, 2024 at 10:46 AM Matthew Ruffell
<matthew.ruffell at canonical.com> 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

Acked-by: Chris Chiu <chris.chiu at canonical.com>