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Message-ID: <4fd38af7-7bf3-7a3c-d150-a187a5098fac@loongson.cn>
Date: Thu, 27 Nov 2025 11:12:45 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: "open list:LOONGARCH" <loongarch@...ts.linux.dev>,
Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson
<seanjc@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/6] KVM: LoongArch: selftests: Add timer test case
On 2025/11/27 上午11:05, Huacai Chen wrote:
> On Thu, Nov 27, 2025 at 10:54 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>>
>>
>>
>> On 2025/11/27 上午10:51, Huacai Chen wrote:
>>> On Thu, Nov 27, 2025 at 10:48 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>>>>
>>>>
>>>>
>>>> On 2025/11/27 上午10:45, Huacai Chen wrote:
>>>>> On Thu, Nov 27, 2025 at 10:37 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 2025/11/27 上午10:09, Huacai Chen wrote:
>>>>>>> On Thu, Nov 27, 2025 at 9:08 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On 2025/11/26 下午9:43, Huacai Chen wrote:
>>>>>>>>> On Mon, Nov 24, 2025 at 10:17 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On 2025/11/24 上午10:03, Huacai Chen wrote:
>>>>>>>>>>> On Mon, Nov 24, 2025 at 9:58 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> On 2025/11/21 下午10:08, Huacai Chen wrote:
>>>>>>>>>>>>> Hi, Bibo,
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Thu, Nov 20, 2025 at 2:58 PM Bibo Mao <maobibo@...ngson.cn> wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> This patchset adds timer test case for LoongArch system, it is based
>>>>>>>>>>>>>> on common arch_timer test case. And it includes one-shot and period mode
>>>>>>>>>>>>>> timer interrupt test, software emulated timer function and time counter
>>>>>>>>>>>>>> test.
>>>>>>>>>>>>> I test this series on top of 6.18-rc6 with Loongson-3A5000, sometimes
>>>>>>>>>>>>> it passes, sometimes I get:
>>>>>>>>>>>>> [root@...ora kvm]# ./arch_timer
>>>>>>>>>>>>> Random seed: 0x6b8b4567
>>>>>>>>>>>>> Guest assert failed, vcpu 2; stage; 0; iter: 1
>>>>>>>>>>>>> ==== Test Assertion Failure ====
>>>>>>>>>>>>> loongarch/arch_timer.c:79: irq_iter == 0
>>>>>>>>>>>>> pid=60138 tid=60142 errno=4 - Interrupted system call
>>>>>>>>>>>>> 1 0x00000001200037cf: test_vcpu_run 于 arch_timer.c:70
>>>>>>>>>>>>> 2 0x00007ffff2449f27: ?? ??:0
>>>>>>>>>>>>> 3 0x00007ffff24c0633: ?? ??:0
>>>>>>>>>>>>> irq_iter = 0x1.
>>>>>>>>>>>>> Guest period timer interrupt was not triggered within the specified
>>>>>>>>>>>>> interval, try to increase the error margin by [-e] option.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Is this as expected, or something is wrong?
>>>>>>>>>>>> There is problem with that. In generic the vCPU task is rescheduled on
>>>>>>>>>>>> other CPUs or preempted, so period timer interrupt is not handled in
>>>>>>>>>>>> specified time.
>>>>>>>>>>> Then this series need to be updated, or problem comes from other places?
>>>>>>>>>> I think this series need be updated, test success criteria with period
>>>>>>>>>> timer need consider this situation. Let me check how to handle this.
>>>>>>>>> Any updates available?
>>>>>>>> It can be solved by modifying udelay() method with get_cycles() or using
>>>>>>>> cpu loop calculation method.
>>>>>>>>
>>>>>>>> --- a/tools/testing/selftests/kvm/include/loongarch/arch_timer.h
>>>>>>>> +++ b/tools/testing/selftests/kvm/include/loongarch/arch_timer.hYes, no common part for it, but it can be a common problem. If other
>>>> architectures have problems they should also modify their own
>>>> __delay(), right?
>>>>>>>> @@ -71,10 +71,17 @@ static inline void timer_irq_disable(void)
>>>>>>>>
>>>>>>>> static inline void __delay(uint64_t cycles)
>>>>>>>> {
>>>>>>>> - uint64_t start = timer_get_cycles();
>>>>>>>> -
>>>>>>>> - while ((timer_get_cycles() - start) < cycles)
>>>>>>>> - cpu_relax();
>>>>>>>> + uint64_t start, next, loops = 0;
>>>>>>>> +
>>>>>>>> + start = timer_get_cycles();
>>>>>>>> + while (loops < cycles) {
>>>>>>>> + next = timer_get_cycles();
>>>>>>>> + /* only count one cycle if VM is preempted */
>>>>>>>> + if (next > start) {
>>>>>>>> + loops++;
>>>>>>>> + start = next;
>>>>>>>> + }
>>>>>>>> + }
>>>>>>>> }
>>>>>>> Looks good. But ARM64 and RISC-V also use a simple implementation of
>>>>>> there is no period test on them.
>>>>> I think the one-shot test can also have this problem if the CPU is
>>>>> preempted for a very long time.
>>>>>
>>>>>>> __delay(). So should this problem be thought of as a common problem?
>>>>>>> If yes, maybe we can keep __delay() as is and wait for the common
>>>>>>> parts to be fixed.
>>>>>> Also there is no common udelay() API, it is arch specific. Someone may
>>>>>> argue that skipping stolen cycles is not generic for __delay(), other
>>>>>> test cases want accurate cycles rather than skipping stolen cycles. It
>>>>>> is timer test case specific.
>>>>>>
>>>>>> Or adding another api __delay_loops() or keep it as is and wait for
>>>>>> other architectures, there should be no common part for it.
>>>>> Yes, no common part for it, but it can be a common problem. If other
>>>>> architectures have problems they should also modify their own
>>>>> __delay(), right?
>>>> yes, what to do then?
>>> Merge window is coming, let's keep it as is. And this problem only
>>> exist when the background load is high (so preemption happens easily),
>>> I think this is not the usual case.
>> I am ok with it. Maybe it can improve in future :)
> OK, all kvm patches are here, you can test whether everything works.
> https://git.kernel.org/pub/scm/linux/kernel/git/chenhuacai/linux-loongson.git/log/?h=loongarch-kvm
>
> And if you want this series be merged together please send V3 asap.
> https://lore.kernel.org/loongarch/20251124035402.3817179-1-maobibo@loongson.cn/T/#t
Thanks for your reminder.
vcpu preempt patch is not so hurry, it is only performance improvement
and it can wait for next round.
Regards
Bibo Mao
>
> Huacai
>
>>
>> Regards
>> Bibo Mao
>>>
>>> Huacai
>>>
>>>>
>>>>>
>>>>> Huacai
>>>>>
>>>>>>
>>>>>> Regards
>>>>>> Bibo Mao
>>>>>>>
>>>>>>> Huacai
>>>>>>>
>>>>>>>>
>>>>>>>> Regards
>>>>>>>> Bibo Mao
>>>>>>>>>
>>>>>>>>> Huacai
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Regards
>>>>>>>>>> Bibo Mao
>>>>>>>>>>>
>>>>>>>>>>> Huacai
>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> Regards
>>>>>>>>>>>> Bibo Mao
>>>>>>>>>>>>>
>>>>>>>>>>>>> Hucai
>>>>>>>>>>>>>
>>>>>>>>>>>>>> ---
>>>>>>>>>>>>>> v2 ... v3:
>>>>>>>>>>>>>> 1. Adjust order about patch 2 and patch 3
>>>>>>>>>>>>>> 2. Add test case with alphabetical order
>>>>>>>>>>>>>> 3. Merge one-shot and period timer interrupt test case into one
>>>>>>>>>>>>>> 4. Only add LoongArch specific modification with common file
>>>>>>>>>>>>>> Makefile.kvm
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> v1 ... v2:
>>>>>>>>>>>>>> 1. Restore PC and PRMD after exception handler
>>>>>>>>>>>>>> 2. Split patch 4 into two small patches with period timer test and
>>>>>>>>>>>>>> time counter test
>>>>>>>>>>>>>> 3. With time counter test, set time count with 0 when create VM. And
>>>>>>>>>>>>>> verify time count starts from 0 in guest code
>>>>>>>>>>>>>> ---
>>>>>>>>>>>>>> Bibo Mao (6):
>>>>>>>>>>>>>> KVM: LoongArch: selftests: Add system registers save and restore on
>>>>>>>>>>>>>> exception
>>>>>>>>>>>>>> KVM: LoongArch: selftests: Add basic interfaces
>>>>>>>>>>>>>> KVM: LoongArch: selftests: Add exception handler register interface
>>>>>>>>>>>>>> KVM: LoongArch: selftests: Add timer interrupt test case
>>>>>>>>>>>>>> KVM: LoongArch: selftests: Add SW emulated timer test
>>>>>>>>>>>>>> KVM: LoongArch: selftests: Add time counter test
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> tools/testing/selftests/kvm/Makefile.kvm | 1 +
>>>>>>>>>>>>>> .../kvm/include/loongarch/arch_timer.h | 84 ++++++++
>>>>>>>>>>>>>> .../kvm/include/loongarch/processor.h | 81 +++++++-
>>>>>>>>>>>>>> .../selftests/kvm/lib/loongarch/exception.S | 6 +
>>>>>>>>>>>>>> .../selftests/kvm/lib/loongarch/processor.c | 47 ++++-
>>>>>>>>>>>>>> .../selftests/kvm/loongarch/arch_timer.c | 194 ++++++++++++++++++
>>>>>>>>>>>>>> 6 files changed, 410 insertions(+), 3 deletions(-)
>>>>>>>>>>>>>> create mode 100644 tools/testing/selftests/kvm/include/loongarch/arch_timer.h
>>>>>>>>>>>>>> create mode 100644 tools/testing/selftests/kvm/loongarch/arch_timer.c
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> base-commit: 23cb64fb76257309e396ea4cec8396d4a1dbae68
>>>>>>>>>>>>>> --
>>>>>>>>>>>>>> 2.39.3
>>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>
>>>>
>>>>
>>
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