Re: [PATCH 3/3] LoongArch: Allow to enable PREEMPT_RT

[Steven Rostedt <rostedt@goodmis.org>]

On Fri,  8 Nov 2024 17:15:45 +0800
Huacai Chen <chenhuacai@loongson.cn> wrote:

> It is really time.
> 
> LoongArch has all the required architecture related changes, that have
> been identified over time, in order to enable PREEMPT_RT. With the recent
> printk changes, the last known road block has been addressed.
> 
> Allow to enable PREEMPT_RT on LoongArch.
> 
> Below are the latency data from cyclictest on a 4-core Loongson-3A5000
> machine, with a "make -j8" kernel building workload in the background.
> 
> 1. PREEMPT kernel with default configuration:
> 
> ./cyclictest -a -t -m -i200 -d0 -p99
> policy: fifo: loadavg: 8.78 8.96 8.64 10/296 64800
> T: 0 ( 4592) P:99 I:200 C:14838617 Min:   3 Act:    6 Avg:    8 Max:    844
> T: 1 ( 4593) P:99 I:200 C:14838765 Min:   3 Act:    9 Avg:    8 Max:    909
> T: 2 ( 4594) P:99 I:200 C:14838510 Min:   3 Act:    7 Avg:    8 Max:    832
> T: 3 ( 4595) P:99 I:200 C:14838631 Min:   3 Act:    8 Avg:    8 Max:    931
> 
> 2. PREEMPT_RT kernel with default configuration:
> 
> ./cyclictest -a -t -m -i200 -d0 -p99
> policy: fifo: loadavg: 10.38 10.47 10.35 9/336 77788
> T: 0 ( 3941) P:99 I:200 C:19439626 Min:   3 Act:   12 Avg:    8 Max:    227
> T: 1 ( 3942) P:99 I:200 C:19439624 Min:   2 Act:   11 Avg:    8 Max:    184
> T: 2 ( 3943) P:99 I:200 C:19439623 Min:   3 Act:    4 Avg:    7 Max:    223
> T: 3 ( 3944) P:99 I:200 C:19439623 Min:   2 Act:   10 Avg:    7 Max:    226
> 
> 3. PREEMPT_RT kernel with tuned configuration:
> 
> ./cyclictest -a -t -m -i200 -d0 -p99
> policy: fifo: loadavg: 10.52 10.66 10.62 12/334 109397
> T: 0 ( 4765) P:99 I:200 C:29335186 Min:   3 Act:    6 Avg:    8 Max:     62
> T: 1 ( 4766) P:99 I:200 C:29335185 Min:   3 Act:   10 Avg:    8 Max:     52
> T: 2 ( 4767) P:99 I:200 C:29335184 Min:   3 Act:    8 Avg:    8 Max:     64
> T: 3 ( 4768) P:99 I:200 C:29335183 Min:   3 Act:   12 Avg:    8 Max:     53
> 
> Main instruments of tuned configuration include: Disable the boot rom
> space in BIOS for kernel, in order to avoid speculative access to low-
> speed memory; Disable CPUFreq scaling; Disable RTC synchronization in
> the ntpd/chronyd service.

Nice! Looks good.

-- Steve

> 
> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
> ---
>  arch/loongarch/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index 3734f5dd9a57..26ed9d925e7f 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -66,6 +66,7 @@ config LOONGARCH
>  	select ARCH_SUPPORTS_LTO_CLANG
>  	select ARCH_SUPPORTS_LTO_CLANG_THIN
>  	select ARCH_SUPPORTS_NUMA_BALANCING
> +	select ARCH_SUPPORTS_RT
>  	select ARCH_USE_BUILTIN_BSWAP
>  	select ARCH_USE_CMPXCHG_LOCKREF
>  	select ARCH_USE_QUEUED_RWLOCKS