scx_lavd implemented 32 and 64 bit versions of a base-2 logarithm
function. This is now also used in rusty. To avoid code duplication,
let's pull it into a shared header.
Note that there is technically a functional change here as we remove the
always inline compiler directive. We instead assume that the compiler
will know best whether or not to inline the function.
Signed-off-by: David Vernet <void@manifault.com>
In user space in rusty, the tuner detects system utilization, and uses
it to inform how we do load balancing, our greedy / direct cpumasks,
etc. Something else we could be doing but currently aren't, is using
system utilization to inform how we dispatch tasks. We currently have a
static, unchanging slice length for the runtime of the program, but this
is inefficient for all scenarios.
Giving a task a long slice length does have advantages, such as
decreasing the number of involuntary context switches, decreasing the
overhead of preemption by doing it less frequently, possibly getting
better cache locality due to a task running on a CPU for a longer amount
of time, etc. On the other hand, long slices can be problematic as well.
When a system is highly utilized, a CPU-hogging task running for too
long can harm interactive tasks. When the system is under-utilized,
those interactive tasks can likely find an idle, or under-utilized core
to run on. When the system is over-utilized, however, they're likely to
have to park in a runqueue.
Thus, in order to better accommodate such scenarios, this patch
implements a rudimentary slice scaling mechanism in scx_rusty. Rather
than having one global, static slice length, we instead have a dynamic,
global slice length that can be changed depending on system utilization.
When over-utilized, we go with a longer slice length, and vice versa for
when the system is under-utilized. With Terraria, this results in
roughly a 50% improvement in mean FPS when playing on an AMD Ryzen 9
7950X, while running Spotify, and stress-ng -c $((4 * $(nproc))).
Signed-off-by: David Vernet <void@manifault.com>
scx_rusty doesn't do terribly well with interactive workloads. In order
to improve the situation, this patch adds support for basic deadline
scheduling in rusty. This approach doesn't incorporate eligibility, and
simply uses a crude avg_runtime tracking approach to scaling a task's
deadline.
In a series of follow-on changes, we'll update the scheduler to use more
indicators for interactivity that affect both slice length, and deadline
calculation.
Signed-off-by: David Vernet <void@manifault.com>
The current Slack URL gives a link to the Slack workspace, but doesn't
include the invite. Update the URL to include the invite URL to make it
easier for people to join the Slack workspace.
Signed-off-by: Daniel Hodges <hodges.daniel.scott@gmail.com>
Let's remove the extraneous copy pasting and use a lookup helper like we
do for task and pcpu context.
Signed-off-by: David Vernet <void@manifault.com>
A LoadEntity gets the load to transfer between two entities by taking
the minimum of their imbalances and reducing its abs value by
xfer_ratio.
In practice self.imbal(), the push node or domain, always has positive
imbalance and other.imbal(), the pull node or domain, always has
negative imbalance, so other.imbal() is always the minimum even though
the abs value of its imbalance might be greater than the abs value of
self.imbal(). It seems like the intent is to take the minimum of the
two absolute values instead to avoid overbalancing at the puller, so
make both values abs.
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Rusty's load balancer calculates load differently based on average
system CPU utilization in create_domain_hierarchy(). At >= 99.999%
utilization, load is the product of a task's weight and duty cycle;
below that, load is the same as the task's duty cycle.
populate_tasks_by_load(), however, always uses the product when
calculating per-task load so that in the sub-99.999% util case, load is
inflated, typically by a factor of 100 with a normal priority task.
Tasks look too heavy to migrate as a result because a single task would
transfer more load than the domain imbalance allows, leading to
significant imbalance in some cases.
Make populate_tasks_by_load() calculate task load the same way as
domain load, checking lb_apply_weight.
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Add extra info to the README for linking building using system libbpf.
It may not be the preferred way of building, but still could be useful
in certain situations such as making changes against a local libbpf
version.
Signed-off-by: Daniel Hodges <hodges.daniel.scott@gmail.com>
When CDPATH is set the fetch_libbpf build script will cd into
the preferred CDPATH directory. This change removes the CDPATH
environment variable so any preferred CDPATH paths are ignored.
The issue can be reproduced with the following steps:
1) mkdir -p /tmp/libbpf
2) CDPATH=/tmp/ meson setup build --prefix /tmp
The build should fail at the fetch_libbpf step.
Signed-off-by: Daniel Hodges <hodges.daniel.scott@gmail.com>
In order to prevent deadlock conditions user-space schedulers need to
perform memory allocations from a pool of pre-allocated memory that will
never be unmapped/reclaimed by the kernel (unevictable memory).
However, there is a special kernel sysctl setting
(vm.compact_unevictable_allowed) that allows kcompactd to reclaim
unevictable memory. This behavior should be prevented by setting
vm.compact_unevictable_allowed = 0, that is what scx_rustland_core does
transparently when a scheduler is started, restoring the previous value
when the scheduler is stopped.
Unfortunately, this is not always doable, especially when running a
scheduler inside a containerized environment or under certain
security/privilege restrictions (e.g., AppArmor confinement).
Therefore, just report a WARNING if we are unable to change this
parameter, instead of considering it a hard-failure, to allow running
scx_rustland_core schedulers also inside such limited environments.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
We're failing in CI with:
/usr/include/string.h:26:10: fatal error: 'bits/libc-header-start.h'
file not found
26 | #include <bits/libc-header-start.h>
This header is apparently shipped with the gcc-multilib Ubuntu package,
according to a Stack Overflow post. Let's see if this fixes CI.
Signed-off-by: David Vernet <void@manifault.com>
The current code replenishes the task's time slice whenever the task
becomes ops.running(). However, there is a case where such behavior can
starve the other tasks, causing the watchdog timeout error. One (if not
all) such case is when a task is preempted while running by the higher
scheduler class (e.g., RT, DL). In such a case, the task will be transit
in a cycle of ops.running() -> ops.stopping() -> ops.running() -> etc.
Whenever it becomes re-running, it will be placed at the head of local
DSQ and ops.running() will renew its time slice. Hence, in the worst
case, the task can run forever since its time slice is never exhausted.
The fix is assigning the time slice only once by checking if the time
slice is calculated before.
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Changwoo Min <changwoo@igalia.com>
Provide a command line option to print the version of the scheduler and
the scx_rustland_core crate.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Given that rustland_core now supports task preemption and it has been
tested successfully, it's worhtwhile to cut a new version of the crate.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
In Rust c_char can be aliased to i8 or u8, depending on the particular
target architecture.
For example, trying to build scx_lavd on ppc64 triggers the following
error:
error[E0308]: mismatched types
--> src/main.rs:200:38
|
200 | let c_tx_cm: *const c_char = (&tx.comm as *const [i8; 17]) as *const i8;
| ------------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `*const u8`, found `*const i8`
| |
| expected due to this
|
= note: expected raw pointer `*const u8`
found raw pointer `*const i8`
To fix this, consistently use c_char instead of assuming it corresponds
to i8.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
In _some_ kernel versions, loading scx_lavd fails with an error of
"bpf_rcu_read_unlock is missing". The usage of
bpf_rcu_read_lock/unlock() in proc_dump_all_tasks() is correct but the
bpf verifier still think bpf_rcu_read_unlock() is missing. The most
plausible reason so far is that the problematic kernel does not have a
commit 6fceea0fa59f ("bpf: Transfer RCU lock state between subprog
calls"), failing inter-procedural analysis between proc_dump_all_tasks()
and submit_task_ctx(). Thus, we force inline submit_task_ctx() (no
inter-procedural analysis by the verifier is necessary) for the time
being.
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Changwoo Min <changwoo@igalia.com>
