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Message-ID: <CAAhV-H7WEMTJWROBxm1hYNu2PQWZvBg2xTy5ACeO+E3JaZG1FQ@mail.gmail.com>
Date: Thu, 27 Nov 2025 14:42:52 +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 2:21 PM 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.
> Another method is to modify period timer test case, calling udelay with
> loop times rather than one time, something like this:
> --- a/tools/testing/selftests/kvm/loongarch/arch_timer.c
> +++ b/tools/testing/selftests/kvm/loongarch/arch_timer.c
> @@ -75,7 +75,7 @@ static void guest_test_oneshot_timer(uint32_t cpu)
>
> static void guest_test_period_timer(uint32_t cpu)
> {
> - uint32_t irq_iter;
> + uint32_t irq_iter, config_iter;
> uint64_t us;
> struct test_vcpu_shared_data *shared_data = &vcpu_shared_data[cpu];
>
> @@ -84,7 +84,8 @@ static void guest_test_period_timer(uint32_t cpu)
> us = msecs_to_usecs(test_args.timer_period_ms) +
> test_args.timer_err_margin_us;
> timer_set_next_cmp_ms(test_args.timer_period_ms, true);
> /* Setup a timeout for the interrupt to arrive */
> - udelay(us * test_args.nr_iter);
> + for (config_iter = 0; config_iter < test_args.nr_iter;
> config_iter++)
> + udelay(us);
This can reduce the probability but still cause problem if the
background CPU load is very high. So I suggest keep it as is.
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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