Re: [PATCH v4 3/3] kselftest: Extend vDSO selftest to clock_getres

Christophe Leroy
2019-06-04T13:39:22Z

Le 04/06/2019 à 15:32, Vincenzo Frascino a écrit :
> Hi Christophe,
>
> On 04/06/2019 14:16, Christophe Leroy wrote:
>> Hi Vincenzo
>>
>> Le 28/05/2019 à 13:57, Vincenzo Frascino a écrit :
>>> Hi Michael,
>>>
>>> thank you for your reply.
>>>
>>> On 28/05/2019 07:19, Michael Ellerman wrote:
>>>> Vincenzo Frascino <vincenzo.frascino@arm.com> writes:
>>>>
>>>>> The current version of the multiarch vDSO selftest verifies only
>>>>> gettimeofday.
>>>>>
>>>>> Extend the vDSO selftest to clock_getres, to verify that the
>>>>> syscall and the vDSO library function return the same information.
>>>>>
>>>>> The extension has been used to verify the hrtimer_resoltion fix.
>>>>
>>>> This is passing for me even without patch 1 applied, shouldn't it fail
>>>> without the fix? What am I missing?
>>>>
>>>
>>> This is correct, because during the refactoring process I missed an "n" :)
>>>
>>> if·((x.tv_sec·!=·y.tv_sec)·||·(x.tv_sec·!=·y.tv_sec))
>>>
>>> Should be:
>>>
>>> if·((x.tv_sec·!=·y.tv_sec)·||·(x.tv_nsec·!=·y.tv_nsec))
>>>
>>> My mistake, I am going to fix the test and re-post v5 of this set.
>>>
>>> Without my patch if you pass "highres=off" to the kernel (as a command line
>>> parameter) it leads to a broken implementation of clock_getres since the value
>>> of CLOCK_REALTIME_RES does not change at runtime.
>>>
>>> Expected result (with highres=off):
>>>
>>> # uname -r
>>> 5.2.0-rc2
>>> # ./vdso_clock_getres
>>> clock_id: CLOCK_REALTIME [FAIL]
>>> clock_id: CLOCK_BOOTTIME [PASS]
>>> clock_id: CLOCK_TAI [PASS]
>>> clock_id: CLOCK_REALTIME_COARSE [PASS]
>>> clock_id: CLOCK_MONOTONIC [FAIL]
>>> clock_id: CLOCK_MONOTONIC_RAW [PASS]
>>> clock_id: CLOCK_MONOTONIC_COARSE [PASS]
>>>
>>> The reason of this behavior is that the only clocks supported by getres on
>>> powerpc are CLOCK_REALTIME and CLOCK_MONOTONIC, the rest on the clocks use
>>> always syscalls.
>>
>> vdso64 is supposed to implement CLOCK_{REALTIME/MONOTONIC}_COARSE, so I
>> guess it should fail for them too ?
>>
>> Or is your test done on vdso32 ?
>>
>
> Based on what I can see in kernel/vdso64 in 5.2-rc3:
>
> /*
> * Exact prototype of clock_getres()
> *
> * int __kernel_clock_getres(clockid_t clock_id, struct timespec *res);
> *
> */
> V_FUNCTION_BEGIN(__kernel_clock_getres)
> .cfi_startproc
> /* Check for supported clock IDs */
> cmpwi cr0,r3,CLOCK_REALTIME
> cmpwi cr1,r3,CLOCK_MONOTONIC
> cror cr0*4+eq,cr0*4+eq,cr1*4+eq
> bne cr0,99f
>
> li r3,0
> cmpldi cr0,r4,0
> crclr cr0*4+so
> beqlr
> lis r5,CLOCK_REALTIME_RES@h
> ori r5,r5,CLOCK_REALTIME_RES@l
> std r3,TSPC64_TV_SEC(r4)
> std r5,TSPC64_TV_NSEC(r4)
> blr
>
> /*
> * syscall fallback
> */
> 99:
> li r0,__NR_clock_getres
> sc
> blr
> .cfi_endproc
> V_FUNCTION_END(__kernel_clock_getres)
>
> it does not seem so for what concerns vdso64. I did run again the test both on
> ppc and ppc64 qemu instances and the result is the same to what I reported in
> this thread.
>
> Am I missing something?

I was thinking about
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5c929885f1bb
but apparently clock_getres() was left aside. Should we do something
about it ?

Christophe

>
>> Christophe
>>
>>>
>>>> # uname -r
>>>> 5.2.0-rc2-gcc-8.2.0
>>>>
>>>> # ./vdso_clock_getres
>>>> clock_id: CLOCK_REALTIME [PASS]
>>>> clock_id: CLOCK_BOOTTIME [PASS]
>>>> clock_id: CLOCK_TAI [PASS]
>>>> clock_id: CLOCK_REALTIME_COARSE [PASS]
>>>> clock_id: CLOCK_MONOTONIC [PASS]
>>>> clock_id: CLOCK_MONOTONIC_RAW [PASS]
>>>> clock_id: CLOCK_MONOTONIC_COARSE [PASS]
>>>>
>>>> cheers
>>>>
>>>>> Cc: Shuah Khan <shuah@kernel.org>
>>>>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
>>>>> ---
>>>>>
>>>>> Note: This patch is independent from the others in this series, hence it
>>>>> can be merged singularly by the kselftest maintainers.
>>>>>
>>>>> tools/testing/selftests/vDSO/Makefile | 2 +
>>>>> .../selftests/vDSO/vdso_clock_getres.c | 124 ++++++++++++++++++
>>>>> 2 files changed, 126 insertions(+)
>>>>> create mode 100644 tools/testing/selftests/vDSO/vdso_clock_getres.c
>>>
>