linux-kernel - Re: [PATCH v3 0/6] KVM: LoongArch: selftests: Add timer test case

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Message-ID: <0e125e35-8044-a6ce-998f-1221da0e827d@loongson.cn>
Date: Thu, 27 Nov 2025 09:05:51 +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 2025/11/26 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.h
@@ -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;
+               }
+       }
  }

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
>>>>>>
>>>>
>>