[PATCH v4 0/4] defconfig: drop RT_GROUP_SCHED=y

[PATCH v4 0/4] defconfig: drop RT_GROUP_SCHED=y

[Celeste Liu]

For cgroup v1, if turned on, and there's any cgroup in the "cpu" hierarchy it
needs an RT budget assigned, otherwise the processes in it will not be able to
get RT at all. The problem with RT group scheduling is that it requires the
budget assigned but there's no way we could assign a default budget, since the
values to assign are both upper and lower time limits, are absolute, and need to
be sum up to < 1 for each individal cgroup. That means we cannot really come up
with values that would work by default in the general case.[1]

For cgroup v2, it's almost unusable as well. If it turned on, the cpu controller
can only be enabled when all RT processes are in the root cgroup. But it will
lose the benefits of cgroup v2 if all RT process were placed in the same cgroup.

Red Hat, Gentoo, Arch Linux and Debian all disable it. systemd also doesn't
support it.[2]

[1]: https://bugzilla.redhat.com/show_bug.cgi?id=1229700
[2]: https://github.com/systemd/systemd/issues/13781#issuecomment-549164383

---
Changes in v4:
- Update Acked-by
- Link to v3: https://lore.kernel.org/r/20240910-fix-riscv-rt_group_sched-v3-0-486e75e5ae6d@gmail.com

Changes in v3:
- Remove Fixes: tag because of it's not suitable.
- Link to v2: https://lore.kernel.org/r/20240823-fix-riscv-rt_group_sched-v2-0-e4dbae24f7e1@gmail.com

Changes in v2:
* Remove MIPS and PowerPC patch because of merged.
* Link to v1: https://lore.kernel.org/lkml/20240530111947.549474-8-CoelacanthusHex@gmail.com/T

Celeste Liu (6):
  riscv: defconfig: drop RT_GROUP_SCHED=y
  loongarch: defconfig: drop RT_GROUP_SCHED=y
  sh: defconfig: drop RT_GROUP_SCHED=y from sdk7786/urquell
  arm: defconfig: drop RT_GROUP_SCHED=y from bcm2855/tegra/omap2plus

 arch/arm/configs/bcm2835_defconfig         | 1 -
 arch/arm/configs/omap2plus_defconfig       | 1 -
 arch/arm/configs/tegra_defconfig           | 1 -
 arch/loongarch/configs/loongson3_defconfig | 1 -
 arch/riscv/configs/defconfig               | 1 -
 arch/sh/configs/sdk7786_defconfig          | 1 -
 arch/sh/configs/urquell_defconfig          | 1 -
 7 files changed, 7 deletions(-)

--
2.45.1

---
Celeste Liu (4):
      riscv: defconfig: drop RT_GROUP_SCHED=y
      loongarch: defconfig: drop RT_GROUP_SCHED=y
      sh: defconfig: drop RT_GROUP_SCHED=y from sdk7786/urquell
      arm: defconfig: drop RT_GROUP_SCHED=y from bcm2835/tegra/omap2plus

 arch/arm/configs/bcm2835_defconfig         | 1 -
 arch/arm/configs/omap2plus_defconfig       | 1 -
 arch/arm/configs/tegra_defconfig           | 1 -
 arch/loongarch/configs/loongson3_defconfig | 1 -
 arch/riscv/configs/defconfig               | 1 -
 arch/sh/configs/sdk7786_defconfig          | 1 -
 arch/sh/configs/urquell_defconfig          | 1 -
 7 files changed, 7 deletions(-)
---
base-commit: 0e287d31b62bb53ad81d5e59778384a40f8b6f56
change-id: 20240627-fix-riscv-rt_group_sched-d2e014be48da

Best regards,
-- 
Celeste Liu <uwu@coelacanthus.name>

[PATCH v4 1/4] riscv: defconfig: drop RT_GROUP_SCHED=y

[Celeste Liu]

Commit ba6cfef057e1 ("riscv: enable Docker requirements in defconfig")
introduced it because of Docker, but Docker has removed this requirement
since [1] (2023-04-19).

For cgroup v1, if turned on, and there's any cgroup in the "cpu" hierarchy it
needs an RT budget assigned, otherwise the processes in it will not be able to
get RT at all. The problem with RT group scheduling is that it requires the
budget assigned but there's no way we could assign a default budget, since the
values to assign are both upper and lower time limits, are absolute, and need to
be sum up to < 1 for each individal cgroup. That means we cannot really come up
with values that would work by default in the general case.[2]

For cgroup v2, it's almost unusable as well. If it turned on, the cpu controller
can only be enabled when all RT processes are in the root cgroup. But it will
lose the benefits of cgroup v2 if all RT process were placed in the same cgroup.

Red Hat, Gentoo, Arch Linux and Debian all disable it. systemd also doesn't
support it.[3]

[1]: https://github.com/moby/moby/commit/005150ed69c540fb0b5323e0f2208608c1204536
[2]: https://bugzilla.redhat.com/show_bug.cgi?id=1229700
[3]: https://github.com/systemd/systemd/issues/13781#issuecomment-549164383

Acked-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Acked-by: Charlie Jenkins <charlie@rivosinc.com>
Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
---
 arch/riscv/configs/defconfig | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/riscv/configs/defconfig b/arch/riscv/configs/defconfig
index b4a37345703eb35757419aa5a2b057c82ed22fda..46b8fb30726858a945a24097773174961c2f4d10 100644
--- a/arch/riscv/configs/defconfig
+++ b/arch/riscv/configs/defconfig
@@ -10,7 +10,6 @@ CONFIG_MEMCG=y
 CONFIG_BLK_CGROUP=y
 CONFIG_CGROUP_SCHED=y
 CONFIG_CFS_BANDWIDTH=y
-CONFIG_RT_GROUP_SCHED=y
 CONFIG_CGROUP_PIDS=y
 CONFIG_CGROUP_FREEZER=y
 CONFIG_CGROUP_HUGETLB=y

-- 
2.48.0

[PATCH v4 2/4] loongarch: defconfig: drop RT_GROUP_SCHED=y

[Celeste Liu]

For cgroup v1, if turned on, and there's any cgroup in the "cpu" hierarchy it
needs an RT budget assigned, otherwise the processes in it will not be able to
get RT at all. The problem with RT group scheduling is that it requires the
budget assigned but there's no way we could assign a default budget, since the
values to assign are both upper and lower time limits, are absolute, and need to
be sum up to < 1 for each individal cgroup. That means we cannot really come up
with values that would work by default in the general case.[1]

For cgroup v2, it's almost unusable as well. If it turned on, the cpu controller
can only be enabled when all RT processes are in the root cgroup. But it will
lose the benefits of cgroup v2 if all RT process were placed in the same cgroup.

Red Hat, Gentoo, Arch Linux and Debian all disable it. systemd also doesn't
support it.[2]

[1]: https://bugzilla.redhat.com/show_bug.cgi?id=1229700
[2]: https://github.com/systemd/systemd/issues/13781#issuecomment-549164383

Reviewed-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
---
 arch/loongarch/configs/loongson3_defconfig | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/loongarch/configs/loongson3_defconfig b/arch/loongarch/configs/loongson3_defconfig
index 4dffc90192f7816074c3bd4b55c12159d5757676..4387bcec8f484173e5367456a69f6a7f03595d46 100644
--- a/arch/loongarch/configs/loongson3_defconfig
+++ b/arch/loongarch/configs/loongson3_defconfig
@@ -24,7 +24,6 @@ CONFIG_NUMA_BALANCING=y
 CONFIG_MEMCG=y
 CONFIG_BLK_CGROUP=y
 CONFIG_CFS_BANDWIDTH=y
-CONFIG_RT_GROUP_SCHED=y
 CONFIG_CGROUP_PIDS=y
 CONFIG_CGROUP_RDMA=y
 CONFIG_CGROUP_FREEZER=y

-- 
2.48.0

[PATCH v4 3/4] sh: defconfig: drop RT_GROUP_SCHED=y from sdk7786/urquell

[Celeste Liu]

For cgroup v1, if turned on, and there's any cgroup in the "cpu" hierarchy it
needs an RT budget assigned, otherwise the processes in it will not be able to
get RT at all. The problem with RT group scheduling is that it requires the
budget assigned but there's no way we could assign a default budget, since the
values to assign are both upper and lower time limits, are absolute, and need to
be sum up to < 1 for each individal cgroup. That means we cannot really come up
with values that would work by default in the general case.[1]

For cgroup v2, it's almost unusable as well. If it turned on, the cpu controller
can only be enabled when all RT processes are in the root cgroup. But it will
lose the benefits of cgroup v2 if all RT process were placed in the same cgroup.

Red Hat, Gentoo, Arch Linux and Debian all disable it. systemd also doesn't
support it.[2]

[1]: https://bugzilla.redhat.com/show_bug.cgi?id=1229700
[2]: https://github.com/systemd/systemd/issues/13781#issuecomment-549164383

Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
---
 arch/sh/configs/sdk7786_defconfig | 1 -
 arch/sh/configs/urquell_defconfig | 1 -
 2 files changed, 2 deletions(-)

diff --git a/arch/sh/configs/sdk7786_defconfig b/arch/sh/configs/sdk7786_defconfig
index 07894f13441ef622c3af8d8f4b5770c2ab66bcd8..7a6efd5b4a62463381005072a679a8ce022a2ef9 100644
--- a/arch/sh/configs/sdk7786_defconfig
+++ b/arch/sh/configs/sdk7786_defconfig
@@ -17,7 +17,6 @@ CONFIG_CPUSETS=y
 CONFIG_CGROUP_CPUACCT=y
 CONFIG_CGROUP_MEMCG=y
 CONFIG_CGROUP_SCHED=y
-CONFIG_RT_GROUP_SCHED=y
 CONFIG_BLK_CGROUP=y
 CONFIG_RELAY=y
 CONFIG_NAMESPACES=y
diff --git a/arch/sh/configs/urquell_defconfig b/arch/sh/configs/urquell_defconfig
index 00ef62133b04ded8d0b4221f11e0adafde99d386..9cf4a719001ea5ef4b031c1bbbf8098e8af5a2b2 100644
--- a/arch/sh/configs/urquell_defconfig
+++ b/arch/sh/configs/urquell_defconfig
@@ -15,7 +15,6 @@ CONFIG_CPUSETS=y
 CONFIG_CGROUP_CPUACCT=y
 CONFIG_CGROUP_MEMCG=y
 CONFIG_CGROUP_SCHED=y
-CONFIG_RT_GROUP_SCHED=y
 CONFIG_BLK_DEV_INITRD=y
 CONFIG_PROFILING=y
 CONFIG_MODULES=y

-- 
2.48.0

[PATCH v4 4/4] arm: defconfig: drop RT_GROUP_SCHED=y from bcm2835/tegra/omap2plus

[Celeste Liu]

Commit 673ce00c5d6c ("ARM: omap2plus_defconfig: Add support for distros
with systemd") said it's because of recommendation from systemd. But
systemd changed their recommendation later.[1]

For cgroup v1, if turned on, and there's any cgroup in the "cpu" hierarchy it
needs an RT budget assigned, otherwise the processes in it will not be able to
get RT at all. The problem with RT group scheduling is that it requires the
budget assigned but there's no way we could assign a default budget, since the
values to assign are both upper and lower time limits, are absolute, and need to
be sum up to < 1 for each individal cgroup. That means we cannot really come up
with values that would work by default in the general case.[2]

For cgroup v2, it's almost unusable as well. If it turned on, the cpu controller
can only be enabled when all RT processes are in the root cgroup. But it will
lose the benefits of cgroup v2 if all RT process were placed in the same cgroup.

Red Hat, Gentoo, Arch Linux and Debian all disable it. systemd also doesn't
support it.

[1]: https://github.com/systemd/systemd/commit/f4e74be1856b3ac058acbf1be321c31d5299f69f
[2]: https://bugzilla.redhat.com/show_bug.cgi?id=1229700

Tested-by: Stefan Wahren <wahrenst@gmx.net>
Acked-by: Kevin Hilman <khilman@baylibre.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
---
 arch/arm/configs/bcm2835_defconfig   | 1 -
 arch/arm/configs/omap2plus_defconfig | 1 -
 arch/arm/configs/tegra_defconfig     | 1 -
 3 files changed, 3 deletions(-)

diff --git a/arch/arm/configs/bcm2835_defconfig b/arch/arm/configs/bcm2835_defconfig
index b5f0bd8dd536990a0726e73a6855d25c1286a768..27dc3bf6b124c2012b7a1a768f2f900f49903cd1 100644
--- a/arch/arm/configs/bcm2835_defconfig
+++ b/arch/arm/configs/bcm2835_defconfig
@@ -7,7 +7,6 @@ CONFIG_BSD_PROCESS_ACCT=y
 CONFIG_BSD_PROCESS_ACCT_V3=y
 CONFIG_LOG_BUF_SHIFT=18
 CONFIG_CFS_BANDWIDTH=y
-CONFIG_RT_GROUP_SCHED=y
 CONFIG_CGROUP_FREEZER=y
 CONFIG_CPUSETS=y
 CONFIG_CGROUP_DEVICE=y
diff --git a/arch/arm/configs/omap2plus_defconfig b/arch/arm/configs/omap2plus_defconfig
index 3a166c2f02bd80634fee3bd8c4579fdbad84ccfa..9cb265c8d4144ea9a41f02640dbc8a06b710323b 100644
--- a/arch/arm/configs/omap2plus_defconfig
+++ b/arch/arm/configs/omap2plus_defconfig
@@ -13,7 +13,6 @@ CONFIG_MEMCG=y
 CONFIG_BLK_CGROUP=y
 CONFIG_CGROUP_SCHED=y
 CONFIG_CFS_BANDWIDTH=y
-CONFIG_RT_GROUP_SCHED=y
 CONFIG_CGROUP_FREEZER=y
 CONFIG_CPUSETS=y
 CONFIG_CGROUP_DEVICE=y
diff --git a/arch/arm/configs/tegra_defconfig b/arch/arm/configs/tegra_defconfig
index d2a094ad360cefefbc3bd35226c5d23eadce42c1..3a9bda2bf422b14085c60b39a2c3df86fe0994bb 100644
--- a/arch/arm/configs/tegra_defconfig
+++ b/arch/arm/configs/tegra_defconfig
@@ -6,7 +6,6 @@ CONFIG_IKCONFIG=y
 CONFIG_IKCONFIG_PROC=y
 CONFIG_CGROUPS=y
 CONFIG_CGROUP_SCHED=y
-CONFIG_RT_GROUP_SCHED=y
 CONFIG_CGROUP_FREEZER=y
 CONFIG_CGROUP_CPUACCT=y
 CONFIG_CGROUP_DEBUG=y

-- 
2.48.0

Re: [PATCH v4 4/4] arm: defconfig: drop RT_GROUP_SCHED=y from bcm2835/tegra/omap2plus

[Florian Fainelli]

On 1/14/25 12:41, Celeste Liu wrote:
> Commit 673ce00c5d6c ("ARM: omap2plus_defconfig: Add support for distros
> with systemd") said it's because of recommendation from systemd. But
> systemd changed their recommendation later.[1]
> 
> For cgroup v1, if turned on, and there's any cgroup in the "cpu" hierarchy it
> needs an RT budget assigned, otherwise the processes in it will not be able to
> get RT at all. The problem with RT group scheduling is that it requires the
> budget assigned but there's no way we could assign a default budget, since the
> values to assign are both upper and lower time limits, are absolute, and need to
> be sum up to < 1 for each individal cgroup. That means we cannot really come up
> with values that would work by default in the general case.[2]
> 
> For cgroup v2, it's almost unusable as well. If it turned on, the cpu controller
> can only be enabled when all RT processes are in the root cgroup. But it will
> lose the benefits of cgroup v2 if all RT process were placed in the same cgroup.
> 
> Red Hat, Gentoo, Arch Linux and Debian all disable it. systemd also doesn't
> support it.
> 
> [1]: https://github.com/systemd/systemd/commit/f4e74be1856b3ac058acbf1be321c31d5299f69f
> [2]: https://bugzilla.redhat.com/show_bug.cgi?id=1229700
> 
> Tested-by: Stefan Wahren <wahrenst@gmx.net>
> Acked-by: Kevin Hilman <khilman@baylibre.com>
> Acked-by: Thierry Reding <treding@nvidia.com>
> Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
> ---
>   arch/arm/configs/bcm2835_defconfig   | 1 -

Acked-by: Florian Fainelli <florian.fainelli@broadcom.com> # 
bcm2835_defconfig
-- 
Florian

Re: [PATCH v4 4/4] arm: defconfig: drop RT_GROUP_SCHED=y from bcm2835/tegra/omap2plus

[Thierry Reding]

[-- Attachment #1: Type: text/plain, Size: 1896 bytes --]

On Wed, Jan 15, 2025 at 04:41:23AM +0800, Celeste Liu wrote:
> Commit 673ce00c5d6c ("ARM: omap2plus_defconfig: Add support for distros
> with systemd") said it's because of recommendation from systemd. But
> systemd changed their recommendation later.[1]
> 
> For cgroup v1, if turned on, and there's any cgroup in the "cpu" hierarchy it
> needs an RT budget assigned, otherwise the processes in it will not be able to
> get RT at all. The problem with RT group scheduling is that it requires the
> budget assigned but there's no way we could assign a default budget, since the
> values to assign are both upper and lower time limits, are absolute, and need to
> be sum up to < 1 for each individal cgroup. That means we cannot really come up
> with values that would work by default in the general case.[2]
> 
> For cgroup v2, it's almost unusable as well. If it turned on, the cpu controller
> can only be enabled when all RT processes are in the root cgroup. But it will
> lose the benefits of cgroup v2 if all RT process were placed in the same cgroup.
> 
> Red Hat, Gentoo, Arch Linux and Debian all disable it. systemd also doesn't
> support it.
> 
> [1]: https://github.com/systemd/systemd/commit/f4e74be1856b3ac058acbf1be321c31d5299f69f
> [2]: https://bugzilla.redhat.com/show_bug.cgi?id=1229700
> 
> Tested-by: Stefan Wahren <wahrenst@gmx.net>
> Acked-by: Kevin Hilman <khilman@baylibre.com>
> Acked-by: Thierry Reding <treding@nvidia.com>
> Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
> ---
>  arch/arm/configs/bcm2835_defconfig   | 1 -
>  arch/arm/configs/omap2plus_defconfig | 1 -
>  arch/arm/configs/tegra_defconfig     | 1 -
>  3 files changed, 3 deletions(-)

Hi Arnd,

is this something that you could pick up? I think so far only the RISC-V
patch was picked up, but nobody seems to feel responsible for the ARM
patch here.

Thierry

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Re: [PATCH v4 4/4] arm: defconfig: drop RT_GROUP_SCHED=y from bcm2835/tegra/omap2plus

[Huacai Chen]

On Fri, Mar 7, 2025 at 3:19 AM Thierry Reding <thierry.reding@gmail.com> wrote:
>
> On Wed, Jan 15, 2025 at 04:41:23AM +0800, Celeste Liu wrote:
> > Commit 673ce00c5d6c ("ARM: omap2plus_defconfig: Add support for distros
> > with systemd") said it's because of recommendation from systemd. But
> > systemd changed their recommendation later.[1]
> >
> > For cgroup v1, if turned on, and there's any cgroup in the "cpu" hierarchy it
> > needs an RT budget assigned, otherwise the processes in it will not be able to
> > get RT at all. The problem with RT group scheduling is that it requires the
> > budget assigned but there's no way we could assign a default budget, since the
> > values to assign are both upper and lower time limits, are absolute, and need to
> > be sum up to < 1 for each individal cgroup. That means we cannot really come up
> > with values that would work by default in the general case.[2]
> >
> > For cgroup v2, it's almost unusable as well. If it turned on, the cpu controller
> > can only be enabled when all RT processes are in the root cgroup. But it will
> > lose the benefits of cgroup v2 if all RT process were placed in the same cgroup.
> >
> > Red Hat, Gentoo, Arch Linux and Debian all disable it. systemd also doesn't
> > support it.
> >
> > [1]: https://github.com/systemd/systemd/commit/f4e74be1856b3ac058acbf1be321c31d5299f69f
> > [2]: https://bugzilla.redhat.com/show_bug.cgi?id=1229700
> >
> > Tested-by: Stefan Wahren <wahrenst@gmx.net>
> > Acked-by: Kevin Hilman <khilman@baylibre.com>
> > Acked-by: Thierry Reding <treding@nvidia.com>
> > Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
> > ---
> >  arch/arm/configs/bcm2835_defconfig   | 1 -
> >  arch/arm/configs/omap2plus_defconfig | 1 -
> >  arch/arm/configs/tegra_defconfig     | 1 -
> >  3 files changed, 3 deletions(-)
>
> Hi Arnd,
>
> is this something that you could pick up? I think so far only the RISC-V
> patch was picked up, but nobody seems to feel responsible for the ARM
> patch here.
I will take the LoongArch patch, but may be squashed to another one
about config file update.

Huacai

>
> Thierry

Re: [PATCH v4 4/4] arm: defconfig: drop RT_GROUP_SCHED=y from bcm2835/tegra/omap2plus

[Arnd Bergmann]

On Thu, Mar 6, 2025, at 20:19, Thierry Reding wrote:
> On Wed, Jan 15, 2025 at 04:41:23AM +0800, Celeste Liu wrote:
>> ---
>>  arch/arm/configs/bcm2835_defconfig   | 1 -
>>  arch/arm/configs/omap2plus_defconfig | 1 -
>>  arch/arm/configs/tegra_defconfig     | 1 -
>>  3 files changed, 3 deletions(-)
>
> Hi Arnd,
>
> is this something that you could pick up? I think so far only the RISC-V
> patch was picked up, but nobody seems to feel responsible for the ARM
> patch here.

I've merged it now after going through stuff in my inbox. It's
generally ok for patches like this one to be forwarded to
soc@lists.linux.dev where they end up in patchwork for me to apply,
in case you don't want it to get lost.

     Arnd

Re: [PATCH v4 0/4] defconfig: drop RT_GROUP_SCHED=y

[patchwork-bot+linux-riscv]

Hello:

This series was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <palmer@rivosinc.com>:

On Wed, 15 Jan 2025 04:41:19 +0800 you wrote:
> For cgroup v1, if turned on, and there's any cgroup in the "cpu" hierarchy it
> needs an RT budget assigned, otherwise the processes in it will not be able to
> get RT at all. The problem with RT group scheduling is that it requires the
> budget assigned but there's no way we could assign a default budget, since the
> values to assign are both upper and lower time limits, are absolute, and need to
> be sum up to < 1 for each individal cgroup. That means we cannot really come up
> with values that would work by default in the general case.[1]
> 
> [...]

Here is the summary with links:
  - [v4,1/4] riscv: defconfig: drop RT_GROUP_SCHED=y
    https://git.kernel.org/riscv/c/26f2d6de4179
  - [v4,2/4] loongarch: defconfig: drop RT_GROUP_SCHED=y
    (no matching commit)
  - [v4,3/4] sh: defconfig: drop RT_GROUP_SCHED=y from sdk7786/urquell
    (no matching commit)
  - [v4,4/4] arm: defconfig: drop RT_GROUP_SCHED=y from bcm2835/tegra/omap2plus
    (no matching commit)

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html