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

Vincenzo Frascino
2019-06-04T13:43:50Z

On 04/06/2019 14:39, Christophe Leroy wrote:
>
>
> 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 ?
>

Sure, but I would like this series to be merged first (since the topic is
different). I am happy, after that, to push a separate one on top that addresses
the problem.

Please let me know if it works for you and Michael.

> 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
>>>>
>>

--
Regards,
Vincenzo