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Message-ID: <CAAhV-H7VMAwcdG3LqKL2sdS==G5=ARWtwBcYq65y15+0aWUMtQ@mail.gmail.com>
Date: Thu, 27 Nov 2025 10:45:46 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
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 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.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;
> >> + }
> >> + }
> >> }
> > 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?
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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