From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- Documentation/gpu/amdgpu/process-isolation.rst | 60 ++++++++++++++++++++++++++ 1 file changed, 60 insertions(+) create mode 100644 Documentation/gpu/amdgpu/process-isolation.rst (limited to 'Documentation/gpu/amdgpu/process-isolation.rst') diff --git a/Documentation/gpu/amdgpu/process-isolation.rst b/Documentation/gpu/amdgpu/process-isolation.rst new file mode 100644 index 000000000..03c4288aa --- /dev/null +++ b/Documentation/gpu/amdgpu/process-isolation.rst @@ -0,0 +1,60 @@ +.. _amdgpu-process-isolation: +.. SPDX-License-Identifier: GPL-2.0 + +========================= + AMDGPU Process Isolation +========================= + +The AMDGPU driver includes a feature that enables automatic process isolation on the graphics engine. This feature serializes access to the graphics engine and adds a cleaner shader which clears the Local Data Store (LDS) and General Purpose Registers (GPRs) between jobs. All processes using the GPU, including both graphics and compute workloads, are serialized when this feature is enabled. On GPUs that support partitionable graphics engines, this feature can be enabled on a per-partition basis. + +In addition, there is an interface to manually run the cleaner shader when the use of the GPU is complete. This may be preferable in some use cases, such as a single-user system where the login manager triggers the cleaner shader when the user logs out. + +Process Isolation +================= + +The `run_cleaner_shader` and `enforce_isolation` sysfs interfaces allow users to manually execute the cleaner shader and control the process isolation feature, respectively. + +Partition Handling +------------------ + +The `enforce_isolation` file in sysfs can be used to enable process isolation and automatic shader cleanup between processes. On GPUs that support graphics engine partitioning, this can be enabled per partition. The partition and its current setting (0 disabled, 1 enabled) can be read from sysfs. On GPUs that do not support graphics engine partitioning, only a single partition will be present. Writing 1 to the partition position enables enforce isolation, writing 0 disables it. + +Example of enabling enforce isolation on a GPU with multiple partitions: + +.. code-block:: console + + $ echo 1 0 1 0 > /sys/class/drm/card0/device/enforce_isolation + $ cat /sys/class/drm/card0/device/enforce_isolation + 1 0 1 0 + +The output indicates that enforce isolation is enabled on zeroth and second partition and disabled on first and third partition. + +For devices with a single partition or those that do not support partitions, there will be only one element: + +.. code-block:: console + + $ echo 1 > /sys/class/drm/card0/device/enforce_isolation + $ cat /sys/class/drm/card0/device/enforce_isolation + 1 + +Cleaner Shader Execution +======================== + +The driver can trigger a cleaner shader to clean up the LDS and GPR state on the graphics engine. When process isolation is enabled, this happens automatically between processes. In addition, there is a sysfs file to manually trigger cleaner shader execution. + +To manually trigger the execution of the cleaner shader, write `0` to the `run_cleaner_shader` sysfs file: + +.. code-block:: console + + $ echo 0 > /sys/class/drm/card0/device/run_cleaner_shader + +For multi-partition devices, you can specify the partition index when triggering the cleaner shader: + +.. code-block:: console + + $ echo 0 > /sys/class/drm/card0/device/run_cleaner_shader # For partition 0 + $ echo 1 > /sys/class/drm/card0/device/run_cleaner_shader # For partition 1 + $ echo 2 > /sys/class/drm/card0/device/run_cleaner_shader # For partition 2 + # ... and so on for each partition + +This command initiates the cleaner shader, which will run and complete before any new tasks are scheduled on the GPU. -- cgit v1.3.1