linux-kernel - Re: [PATCH] LoongArch: time: Fix the issue of high cpu usage of vcpu threads in virtual machines

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAAhV-H7pXxFR8PnAOv8CirotXUSPgbb7AEsHU0VGh_YMFFoyJA@mail.gmail.com>
Date: Tue, 12 Aug 2025 19:17:53 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Xianglai Li <lixianglai@...ngson.cn>
Cc: WANG Xuerui <kernel@...0n.name>, Thomas Gleixner <tglx@...utronix.de>, 
	Peter Zijlstra <peterz@...radead.org>, Bibo Mao <maobibo@...ngson.cn>, 
	Song Gao <gaosong@...ngson.cn>, Tianrui Zhao <zhaotianrui@...ngson.cn>, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: time: Fix the issue of high cpu usage of vcpu
 threads in virtual machines

Hi, Xianglai,

There is something that can be improved.

On Tue, Aug 12, 2025 at 5:24 PM Xianglai Li <lixianglai@...ngson.cn> wrote:
>
> When the cpu is offline, the timer under loongarch is not correctly closed,
> resulting in an excessively high cpu usage rate of the offline vcpu thread
> in the virtual machine.
>
> To correctly close the timer, we have made the following modifications:
>
> Register the cpu hotplug timer start event for loongarch.This event will
> be called to close the timer when the cpu is offline.
>
> Clear the timer interrupt when the timer is turned off
>
> Signed-off-by: Xianglai Li <lixianglai@...ngson.cn>
> ---
>  arch/loongarch/kernel/time.c | 20 ++++++++++++++++++++
>  include/linux/cpuhotplug.h   |  1 +
>  2 files changed, 21 insertions(+)
>
> diff --git a/arch/loongarch/kernel/time.c b/arch/loongarch/kernel/time.c
> index 367906b10f81..4daa11512eba 100644
> --- a/arch/loongarch/kernel/time.c
> +++ b/arch/loongarch/kernel/time.c
> @@ -12,6 +12,7 @@
>  #include <linux/kernel.h>
>  #include <linux/sched_clock.h>
>  #include <linux/spinlock.h>
> +#include <linux/cpu.h>
>
>  #include <asm/cpu-features.h>
>  #include <asm/loongarch.h>
> @@ -86,6 +87,9 @@ static int constant_set_state_shutdown(struct clock_event_device *evt)
>         timer_config &= ~CSR_TCFG_EN;
>         csr_write64(timer_config, LOONGARCH_CSR_TCFG);
>
> +       /* Clear Timer Interrupt */
> +       write_csr_tintclear(CSR_TINTCLR_TI);
> +
>         raw_spin_unlock(&state_lock);
>
>         return 0;
> @@ -208,8 +212,17 @@ int __init constant_clocksource_init(void)
>         return res;
>  }
>
> +static int arch_timer_dying_cpu(unsigned int cpu)
We can use arch_timer_dying() for short. And then add an
arch_timer_starting() like this:

static int arch_timer_starting(unsigned int cpu)
{
        set_csr_ecfg(ECFGF_TIMER);

        return 0;
}

Though ECFGF_TIMER may be enabled in other places, for syntax we need it here.

> +{
> +       constant_set_state_shutdown(NULL);
> +
> +       return 0;
> +}
> +
>  void __init time_init(void)
>  {
> +       int err;
> +
>         if (!cpu_has_cpucfg)
>                 const_clock_freq = cpu_clock_freq;
>         else
> @@ -220,4 +233,11 @@ void __init time_init(void)
>         constant_clockevent_init();
>         constant_clocksource_init();
>         pv_time_init();
> +
> +       err = cpuhp_setup_state_nocalls(CPUHP_AP_LOONGARCH_ARCH_TIMER_STARTING,
> +                                       "loongarch/timer:starting",
> +                                       NULL, arch_timer_dying_cpu);
Then we need use cpuhp_setup_state() here, because we have a startup
function now.

And "loongarch/timer:starting" should be
"clockevents/loongarch/timer:starting" like others.

And the whole should be moved to the last of
constant_clockevent_init() because it is clockevent specific.

> +       if (err)
> +               pr_info("cpu hotplug event register failed");
This is not so useful, because the error isn't fatal.


Huacai

> +
>  }
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index edfa61d80702..6606c1546afc 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -159,6 +159,7 @@ enum cpuhp_state {
>         CPUHP_AP_PERF_ARM_STARTING,
>         CPUHP_AP_PERF_RISCV_STARTING,
>         CPUHP_AP_ARM_L2X0_STARTING,
> +       CPUHP_AP_LOONGARCH_ARCH_TIMER_STARTING,
>         CPUHP_AP_EXYNOS4_MCT_TIMER_STARTING,
>         CPUHP_AP_ARM_ARCH_TIMER_STARTING,
>         CPUHP_AP_ARM_ARCH_TIMER_EVTSTRM_STARTING,
>
> base-commit: 53e760d8949895390e256e723e7ee46618310361
> --
> 2.39.1
>