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Message-ID: <284da6b1-8703-a9d7-f564-236ade3986a8@loongson.cn>
Date: Thu, 27 Nov 2025 10:45:42 +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?
>
> 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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