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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-18 17:39:57 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-18 17:39:57 +0000
commitdc50eab76b709d68175a358d6e23a5a3890764d3 (patch)
treec754d0390db060af0213ff994f0ac310e4cfd6e9 /Documentation/scheduler
parentAdding debian version 6.6.15-2. (diff)
downloadlinux-dc50eab76b709d68175a358d6e23a5a3890764d3.tar.xz
linux-dc50eab76b709d68175a358d6e23a5a3890764d3.zip
Merging upstream version 6.7.7.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/scheduler')
-rw-r--r--Documentation/scheduler/sched-arch.rst4
-rw-r--r--Documentation/scheduler/sched-capacity.rst13
-rw-r--r--Documentation/scheduler/sched-energy.rst29
-rw-r--r--Documentation/scheduler/sched-rt-group.rst40
4 files changed, 32 insertions, 54 deletions
diff --git a/Documentation/scheduler/sched-arch.rst b/Documentation/scheduler/sched-arch.rst
index 505cd27f9a..ed07efea7d 100644
--- a/Documentation/scheduler/sched-arch.rst
+++ b/Documentation/scheduler/sched-arch.rst
@@ -10,7 +10,7 @@ Context switch
By default, the switch_to arch function is called with the runqueue
locked. This is usually not a problem unless switch_to may need to
take the runqueue lock. This is usually due to a wake up operation in
-the context switch. See arch/ia64/include/asm/switch_to.h for an example.
+the context switch.
To request the scheduler call switch_to with the runqueue unlocked,
you must `#define __ARCH_WANT_UNLOCKED_CTXSW` in a header file
@@ -68,7 +68,5 @@ Possible arch/ problems
Possible arch problems I found (and either tried to fix or didn't):
-ia64 - is safe_halt call racy vs interrupts? (does it sleep?) (See #4a)
-
sparc - IRQs on at this point(?), change local_irq_save to _disable.
- TODO: needs secondary CPUs to disable preempt (See #1)
diff --git a/Documentation/scheduler/sched-capacity.rst b/Documentation/scheduler/sched-capacity.rst
index e2c1cf7431..de414b33dd 100644
--- a/Documentation/scheduler/sched-capacity.rst
+++ b/Documentation/scheduler/sched-capacity.rst
@@ -39,14 +39,15 @@ per Hz, leading to::
-------------------
Two different capacity values are used within the scheduler. A CPU's
-``capacity_orig`` is its maximum attainable capacity, i.e. its maximum
-attainable performance level. A CPU's ``capacity`` is its ``capacity_orig`` to
-which some loss of available performance (e.g. time spent handling IRQs) is
-subtracted.
+``original capacity`` is its maximum attainable capacity, i.e. its maximum
+attainable performance level. This original capacity is returned by
+the function arch_scale_cpu_capacity(). A CPU's ``capacity`` is its ``original
+capacity`` to which some loss of available performance (e.g. time spent
+handling IRQs) is subtracted.
Note that a CPU's ``capacity`` is solely intended to be used by the CFS class,
-while ``capacity_orig`` is class-agnostic. The rest of this document will use
-the term ``capacity`` interchangeably with ``capacity_orig`` for the sake of
+while ``original capacity`` is class-agnostic. The rest of this document will use
+the term ``capacity`` interchangeably with ``original capacity`` for the sake of
brevity.
1.3 Platform examples
diff --git a/Documentation/scheduler/sched-energy.rst b/Documentation/scheduler/sched-energy.rst
index fc853c8cc3..70e2921ef7 100644
--- a/Documentation/scheduler/sched-energy.rst
+++ b/Documentation/scheduler/sched-energy.rst
@@ -359,32 +359,9 @@ in milli-Watts or in an 'abstract scale'.
6.3 - Energy Model complexity
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-The task wake-up path is very latency-sensitive. When the EM of a platform is
-too complex (too many CPUs, too many performance domains, too many performance
-states, ...), the cost of using it in the wake-up path can become prohibitive.
-The energy-aware wake-up algorithm has a complexity of:
-
- C = Nd * (Nc + Ns)
-
-with: Nd the number of performance domains; Nc the number of CPUs; and Ns the
-total number of OPPs (ex: for two perf. domains with 4 OPPs each, Ns = 8).
-
-A complexity check is performed at the root domain level, when scheduling
-domains are built. EAS will not start on a root domain if its C happens to be
-higher than the completely arbitrary EM_MAX_COMPLEXITY threshold (2048 at the
-time of writing).
-
-If you really want to use EAS but the complexity of your platform's Energy
-Model is too high to be used with a single root domain, you're left with only
-two possible options:
-
- 1. split your system into separate, smaller, root domains using exclusive
- cpusets and enable EAS locally on each of them. This option has the
- benefit to work out of the box but the drawback of preventing load
- balance between root domains, which can result in an unbalanced system
- overall;
- 2. submit patches to reduce the complexity of the EAS wake-up algorithm,
- hence enabling it to cope with larger EMs in reasonable time.
+EAS does not impose any complexity limit on the number of PDs/OPPs/CPUs but
+restricts the number of CPUs to EM_MAX_NUM_CPUS to prevent overflows during
+the energy estimation.
6.4 - Schedutil governor
diff --git a/Documentation/scheduler/sched-rt-group.rst b/Documentation/scheduler/sched-rt-group.rst
index 655a096ec8..d685609ed3 100644
--- a/Documentation/scheduler/sched-rt-group.rst
+++ b/Documentation/scheduler/sched-rt-group.rst
@@ -39,10 +39,10 @@ Most notable:
1.1 The problem
---------------
-Realtime scheduling is all about determinism, a group has to be able to rely on
+Real-time scheduling is all about determinism, a group has to be able to rely on
the amount of bandwidth (eg. CPU time) being constant. In order to schedule
-multiple groups of realtime tasks, each group must be assigned a fixed portion
-of the CPU time available. Without a minimum guarantee a realtime group can
+multiple groups of real-time tasks, each group must be assigned a fixed portion
+of the CPU time available. Without a minimum guarantee a real-time group can
obviously fall short. A fuzzy upper limit is of no use since it cannot be
relied upon. Which leaves us with just the single fixed portion.
@@ -50,14 +50,14 @@ relied upon. Which leaves us with just the single fixed portion.
----------------
CPU time is divided by means of specifying how much time can be spent running
-in a given period. We allocate this "run time" for each realtime group which
-the other realtime groups will not be permitted to use.
+in a given period. We allocate this "run time" for each real-time group which
+the other real-time groups will not be permitted to use.
-Any time not allocated to a realtime group will be used to run normal priority
+Any time not allocated to a real-time group will be used to run normal priority
tasks (SCHED_OTHER). Any allocated run time not used will also be picked up by
SCHED_OTHER.
-Let's consider an example: a frame fixed realtime renderer must deliver 25
+Let's consider an example: a frame fixed real-time renderer must deliver 25
frames a second, which yields a period of 0.04s per frame. Now say it will also
have to play some music and respond to input, leaving it with around 80% CPU
time dedicated for the graphics. We can then give this group a run time of 0.8
@@ -70,7 +70,7 @@ needs only about 3% CPU time to do so, it can do with a 0.03 * 0.005s =
of 0.00015s.
The remaining CPU time will be used for user input and other tasks. Because
-realtime tasks have explicitly allocated the CPU time they need to perform
+real-time tasks have explicitly allocated the CPU time they need to perform
their tasks, buffer underruns in the graphics or audio can be eliminated.
NOTE: the above example is not fully implemented yet. We still
@@ -87,18 +87,20 @@ lack an EDF scheduler to make non-uniform periods usable.
The system wide settings are configured under the /proc virtual file system:
/proc/sys/kernel/sched_rt_period_us:
- The scheduling period that is equivalent to 100% CPU bandwidth
+ The scheduling period that is equivalent to 100% CPU bandwidth.
/proc/sys/kernel/sched_rt_runtime_us:
- A global limit on how much time realtime scheduling may use. Even without
- CONFIG_RT_GROUP_SCHED enabled, this will limit time reserved to realtime
- processes. With CONFIG_RT_GROUP_SCHED it signifies the total bandwidth
- available to all realtime groups.
+ A global limit on how much time real-time scheduling may use. This is always
+ less or equal to the period_us, as it denotes the time allocated from the
+ period_us for the real-time tasks. Even without CONFIG_RT_GROUP_SCHED enabled,
+ this will limit time reserved to real-time processes. With
+ CONFIG_RT_GROUP_SCHED=y it signifies the total bandwidth available to all
+ real-time groups.
* Time is specified in us because the interface is s32. This gives an
operating range from 1us to about 35 minutes.
* sched_rt_period_us takes values from 1 to INT_MAX.
- * sched_rt_runtime_us takes values from -1 to (INT_MAX - 1).
+ * sched_rt_runtime_us takes values from -1 to sched_rt_period_us.
* A run time of -1 specifies runtime == period, ie. no limit.
@@ -108,7 +110,7 @@ The system wide settings are configured under the /proc virtual file system:
The default values for sched_rt_period_us (1000000 or 1s) and
sched_rt_runtime_us (950000 or 0.95s). This gives 0.05s to be used by
SCHED_OTHER (non-RT tasks). These defaults were chosen so that a run-away
-realtime tasks will not lock up the machine but leave a little time to recover
+real-time tasks will not lock up the machine but leave a little time to recover
it. By setting runtime to -1 you'd get the old behaviour back.
By default all bandwidth is assigned to the root group and new groups get the
@@ -116,10 +118,10 @@ period from /proc/sys/kernel/sched_rt_period_us and a run time of 0. If you
want to assign bandwidth to another group, reduce the root group's bandwidth
and assign some or all of the difference to another group.
-Realtime group scheduling means you have to assign a portion of total CPU
-bandwidth to the group before it will accept realtime tasks. Therefore you will
-not be able to run realtime tasks as any user other than root until you have
-done that, even if the user has the rights to run processes with realtime
+Real-time group scheduling means you have to assign a portion of total CPU
+bandwidth to the group before it will accept real-time tasks. Therefore you will
+not be able to run real-time tasks as any user other than root until you have
+done that, even if the user has the rights to run processes with real-time
priority!