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Running N CPU-bound tasks on an N CPUs platform:
- with asymmetric CPU capacity
- not being a DynamIq system (i.e. having a PKG level sched domain
without the SD_SHARE_PKG_RESOURCES flag set)
.. might result in a task placement where two tasks run on a big CPU
and none on a little CPU. This placement could be more optimal by
using all CPUs.
Testing platform:
Juno-r2:
- 2 big CPUs (1-2), maximum capacity of 1024
- 4 little CPUs (0,3-5), maximum capacity of 383
Testing workload ([1]):
Spawn 6 CPU-bound tasks. During the first 100ms (step 1), each tasks
is affine to a CPU, except for:
- one little CPU which is left idle.
- one big CPU which has 2 tasks affine.
After the 100ms (step 2), remove the cpumask affinity.
Behavior before the patch:
During step 2, the load balancer running from the idle CPU tags sched
domains as:
- little CPUs: 'group_has_spare'. Cf. group_has_capacity() and
group_is_overloaded(), 3 CPU-bound tasks run on a 4 CPUs
sched-domain, and the idle CPU provides enough spare capacity
regarding the imbalance_pct
- big CPUs: 'group_overloaded'. Indeed, 3 tasks run on a 2 CPUs
sched-domain, so the following path is used:
group_is_overloaded()
\-if (sgs->sum_nr_running <= sgs->group_weight) return true;
The following path which would change the migration type to
'migrate_task' is not taken:
calculate_imbalance()
\-if (env->idle != CPU_NOT_IDLE && env->imbalance == 0)
as the local group has some spare capacity, so the imbalance
is not 0.
The migration type requested is 'migrate_util' and the busiest
runqueue is the big CPU's runqueue having 2 tasks (each having a
utilization of 512). The idle little CPU cannot pull one of these
task as its capacity is too small for the task. The following path
is used:
detach_tasks()
\-case migrate_util:
\-if (util > env->imbalance) goto next;
After the patch:
As the number of failed balancing attempts grows (with
'nr_balance_failed'), progressively make it easier to migrate
a big task to the idling little CPU. A similar mechanism is
used for the 'migrate_load' migration type.
Improvement:
Running the testing workload [1] with the step 2 representing
a ~10s load for a big CPU:
Before patch: ~19.3s
After patch: ~18s (-6.7%)
Similar issue reported at:
https://lore.kernel.org/lkml/20230716014125.139577-1-qyousef@layalina.io/
Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: Qais Yousef <qyousef@layalina.io>
Link: https://lore.kernel.org/r/20231206090043.634697-1-pierre.gondois@arm.com
(cherry picked from commit 3af7524b14198f5159a86692d57a9f28ec9375ce)
Change-Id: I916aa7e56af6addf0eb3a78ec77119324172d9d9
Signed-off-by: John Stultz <jstultz@google.com>
How do I submit patches to Android Common Kernels
-
BEST: Make all of your changes to upstream Linux. If appropriate, backport to the stable releases. These patches will be merged automatically in the corresponding common kernels. If the patch is already in upstream Linux, post a backport of the patch that conforms to the patch requirements below.
- Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux,
additions of
EXPORT_SYMBOL_GPL()require an in-tree modular driver that uses the symbol -- so include the new driver or changes to an existing driver in the same patchset as the export. - When sending patches upstream, the commit message must contain a clear case for why the patch is needed and beneficial to the community. Enabling out-of-tree drivers or functionality is not not a persuasive case.
- Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux,
additions of
-
LESS GOOD: Develop your patches out-of-tree (from an upstream Linux point-of-view). Unless these are fixing an Android-specific bug, these are very unlikely to be accepted unless they have been coordinated with kernel-team@android.com. If you want to proceed, post a patch that conforms to the patch requirements below.
Common Kernel patch requirements
- All patches must conform to the Linux kernel coding standards and pass
scripts/checkpatch.pl - Patches shall not break gki_defconfig or allmodconfig builds for arm, arm64, x86, x86_64 architectures (see https://source.android.com/setup/build/building-kernels)
- If the patch is not merged from an upstream branch, the subject must be tagged with the type of patch:
UPSTREAM:,BACKPORT:,FROMGIT:,FROMLIST:, orANDROID:. - All patches must have a
Change-Id:tag (see https://gerrit-review.googlesource.com/Documentation/user-changeid.html) - If an Android bug has been assigned, there must be a
Bug:tag. - All patches must have a
Signed-off-by:tag by the author and the submitter
Additional requirements are listed below based on patch type
Requirements for backports from mainline Linux: UPSTREAM:, BACKPORT:
- If the patch is a cherry-pick from Linux mainline with no changes at all
- tag the patch subject with
UPSTREAM:. - add upstream commit information with a
(cherry picked from commit ...)line - Example:
- if the upstream commit message is
- tag the patch subject with
important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
- then Joe Smith would upload the patch for the common kernel as
UPSTREAM: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
(cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
Signed-off-by: Joe Smith <joe.smith@foo.org>
- If the patch requires any changes from the upstream version, tag the patch with
BACKPORT:instead ofUPSTREAM:.- use the same tags as
UPSTREAM: - add comments about the changes under the
(cherry picked from commit ...)line - Example:
- use the same tags as
BACKPORT: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
(cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
[joe: Resolved minor conflict in drivers/foo/bar.c ]
Signed-off-by: Joe Smith <joe.smith@foo.org>
Requirements for other backports: FROMGIT:, FROMLIST:,
- If the patch has been merged into an upstream maintainer tree, but has not yet
been merged into Linux mainline
- tag the patch subject with
FROMGIT: - add info on where the patch came from as
(cherry picked from commit <sha1> <repo> <branch>). This must be a stable maintainer branch (not rebased, so don't uselinux-nextfor example). - if changes were required, use
BACKPORT: FROMGIT: - Example:
- if the commit message in the maintainer tree is
- tag the patch subject with
important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
- then Joe Smith would upload the patch for the common kernel as
FROMGIT: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
(cherry picked from commit 878a2fd9de10b03d11d2f622250285c7e63deace
https://git.kernel.org/pub/scm/linux/kernel/git/foo/bar.git test-branch)
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
Signed-off-by: Joe Smith <joe.smith@foo.org>
- If the patch has been submitted to LKML, but not accepted into any maintainer tree
- tag the patch subject with
FROMLIST: - add a
Link:tag with a link to the submittal on lore.kernel.org - add a
Bug:tag with the Android bug (required for patches not accepted into a maintainer tree) - if changes were required, use
BACKPORT: FROMLIST: - Example:
- tag the patch subject with
FROMLIST: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
Link: https://lore.kernel.org/lkml/20190619171517.GA17557@someone.com/
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
Signed-off-by: Joe Smith <joe.smith@foo.org>
Requirements for Android-specific patches: ANDROID:
- If the patch is fixing a bug to Android-specific code
- tag the patch subject with
ANDROID: - add a
Fixes:tag that cites the patch with the bug - Example:
- tag the patch subject with
ANDROID: fix android-specific bug in foobar.c
This is the detailed description of the important fix
Fixes: 1234abcd2468 ("foobar: add cool feature")
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
Signed-off-by: Joe Smith <joe.smith@foo.org>
- If the patch is a new feature
- tag the patch subject with
ANDROID: - add a
Bug:tag with the Android bug (required for android-specific features)
- tag the patch subject with