| Message ID | 20250115-fix-riscv-rt_group_sched-v4-4-607606fe73a5@coelacanthus.name |
|---|---|
| State | New |
| Headers | show |
| Series | defconfig: drop RT_GROUP_SCHED=y | expand |
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
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
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
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
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
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(-)