The primary scheduling domain represents a group of CPUs in the system
where the scheduler will initially attempt to assign tasks. Tasks will
only be dispatched to CPUs within this primary domain until they are
fully utilized, after which tasks may overflow to other available CPUs.
The primary scheduling domain can defined using the option
`--primary-domain CPUMASK` (by default all the CPUs in the system are
used as primary domain).
This change introduces two new special values for the CPUMASK argument:
- `performance`: automatically detect the fastest CPUs in the system
and use them as primary scheduling domain,
- `powersave`: automatically detect the slowest CPUs in the system and
use them as primary scheduling domain.
The current logic only supports creating two groups: fast and slow CPUs.
The fast CPU group is created by excluding CPUs with the lowest
frequency from the overall set, which means that within the fast CPU
group, CPUs may have different maximum frequencies.
When using the `performance` mode the fast CPUs will be used as primary
domain, whereas in `powersave` mode, the slow CPUs will be used instead.
This option is particularly useful in hybrid architectures (with P-cores
and E-cores), as it allows the use of bpfland to prioritize task
scheduling on either P-cores or E-cores, depending on the desired
performance profile.
Example:
- Dell Precision 5480
- CPU: 13th Gen Intel(R) Core(TM) i7-13800H
- P-cores: 0-11 / max freq: 5.2GHz
- E-cores: 12-19 / max freq: 4.0GHz
$ scx_bpfland --primary-domain performance
0[||||||||| 24.5%] 10[|||||||| 22.8%]
1[|||||| 14.9%] 11[||||||||||||| 36.9%]
2[|||||| 16.2%] 12[ 0.0%]
3[||||||||| 25.3%] 13[ 0.0%]
4[||||||||||| 33.3%] 14[ 0.0%]
5[|||| 9.9%] 15[ 0.0%]
6[||||||||||| 31.5%] 16[ 0.0%]
7[||||||| 17.4%] 17[ 0.0%]
8[|||||||| 23.4%] 18[ 0.0%]
9[||||||||| 26.1%] 19[ 0.0%]
Avg power consumption: 3.29W
$ scx_bpfland --primary-domain powersave
0[| 2.5%] 10[ 0.0%]
1[ 0.0%] 11[ 0.0%]
2[ 0.0%] 12[|||| 8.0%]
3[ 0.0%] 13[||||||||||||||||||||| 64.2%]
4[ 0.0%] 14[|||||||||| 29.6%]
5[ 0.0%] 15[||||||||||||||||| 52.5%]
6[ 0.0%] 16[||||||||| 24.7%]
7[ 0.0%] 17[|||||||||| 30.4%]
8[ 0.0%] 18[||||||| 22.4%]
9[ 0.0%] 19[||||| 12.4%]
Avg power consumption: 2.17W
(Info collected from htop and turbostat)
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
While the system is not saturated the scheduler will use the following
strategy to select the next CPU for a task:
- pick the same CPU if it's a full-idle SMT core
- pick any full-idle SMT core in the primary scheduling group that
shares the same L2 cache
- pick any full-idle SMT core in the primary scheduling grouop that
shares the same L3 cache
- pick the same CPU (ignoring SMT)
- pick any idle CPU in the primary scheduling group that shares the
same L2 cache
- pick any idle CPU in the primary scheduling group that shares the
same L3 cache
- pick any idle CPU in the system
While the system is completely saturated (no idle CPUs available), tasks
will be dispatched on the first CPU that becomes available.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
- Allow no-value user attributes which are automatically assigned "true"
when specified.
- Make "top" attribute string "true" instead of bool true for consistency.
Testing for existence is always enough for value-less attributes.
- Don't drop leading "_" from user attribute names when storing in dicts.
Dropping makes things more confusing.
- Add "_om_skip" to scx_layered fields which don't jive well with OM.
scxstats_to_openmetrics.py is updated accordignly and no longer generates
warnings on those fields.
- Examples and README updated accordingly.
After updating scx_layered to be topology aware the nr_cpus field on the
layer was not being updated properly. Update layer growing/shrinking
logic to correctly update the nr_cpus count.
Signed-off-by: Daniel Hodges <hodges.daniel.scott@gmail.com>
- This makes the scheduler side simpler and allows on-demand monitoring.
- OpenMetrics support is dropped for now. Will add a generic tool for it.
- This is a naive conversion. Will be further refined.
scx_layered no longer prints statistics by default. To watch statistics, run
`scx_layered --monitor` while the scheduler is running.
Allow to specify a primary scheduling domain via the new command line
option `--primary-domain CPUMASK`, where CPUMASK can be a hex number of
arbitrary length, representing the CPUs assigned to the domain.
If this option is not specified the scheduler will use all the available
CPUs in the system as primary domain (no behavior change).
Otherwise, if a primary scheduling domain is defined, the scheduler will
try to dispatch tasks only to the CPUs assigned to the primary domain,
until these CPUs are saturated, at which point tasks may overflow to
other available CPUs.
This feature can be used to prioritize certain cores over others and it
can be really effective in systems with heterogeneous cores (e.g.,
hybrid systems with P-cores and E-cores).
== Example (hybrid architecture) ==
Hardware:
- Dell Precision 5480 with 13th Gen Intel(R) Core(TM) i7-13800H
- 6 P-cores 0..5 with 2 CPUs each (CPU from 0..11)
- 8 E-cores 6..13 with 1 CPU each (CPU from 12..19)
== Test ==
WebGL application (https://webglsamples.org/aquarium/aquarium.html):
this allows to generate a steady workload in the system without
over-saturating the CPUs.
Use different scheduler configurations:
- EEVDF (default)
- scx_bpfland using P-cores only (--primary-domain 0x00fff)
- scx_bpfland using E-cores only (--primary-domain 0xff000)
Measure performance (fps) and power consumption (W).
== Result ==
+-----+-----+------+-----+----------+
| min | max | avg | | |
| fps | fps | fps | stdev | power |
+-----------------+-----+-----+------+-------+--------+
| EEVDF | 28 | 34 | 31.0 | 1.73 | 3.5W |
| bpfland-p-cores | 33 | 34 | 33.5 | 0.29 | 3.5W |
| bpfland-e-cores | 25 | 26 | 25.5 | 0.29 | 2.2W |
+-----------------+-----+-----+------+-------+--------+
Using a primary scheduling domain of only P-cores with scx_bpfland
allows to achieve a more stable and predictable level of performance,
with an average of 33.5 fps and an error of ±0.5 fps.
In contrast, using EEVDF results in an average frame rate of 31.0 fps
with an error of ±3.0 fps, indicating slightly less consistency, due to
the fact that tasks are evenly distributed across all the cores in the
system (both slow and fast cores).
On the other hand, using a scheduling domain solely of E-cores with
scx_bpfland results in a lower average frame rate (25.5 fps), though it
maintains a stable performance (error of ±0.5 fps), but the power
consumption is also reduced, averaging 2.2W, compared to 3.5W with
either of the other configurations.
== Conclusion ==
In summary, with this change users have the flexibility to prioritize
scheduling on performance cores for better performance and consistency,
or prioritize energy efficient cores for reduced power consumption, on
hybrid architectures.
Moreover, this feature can also be used to minimize the number of cores
used by the scheduler, until they reach full capacity. This capability
can be useful for reducing power consumption even in homogeneous systems
or for conducting scheduling experiments with smaller sets of cores,
provided the system is not overcommitted.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Abbreviate the statistics reported to stdout and remove the slice_ms
metric: this metric can be easily derived from slice_ns, slice_ns_min
and nr_wait, which is already reported to stdout.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Layer matching currently takes a large number of bpf instructions.
Moving layer matching to a global function will reduce the overall
instruction count and allow for other layer matching methods such as
glob.
Signed-off-by: Daniel Hodges <hodges.daniel.scott@gmail.com>
Put a performance-critical task to a performance critical queue and a
regular task to a regular queue.
Signed-off-by: Changwoo Min <changwoo@igalia.com>
