[rcu:dev.2020.05.26a 56/72] refperf.c:undefined reference to `__umoddi3'

[rcu:dev.2020.05.26a 56/72] refperf.c:undefined reference to `__umoddi3'

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 1260 bytes --]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2020.05.26a
head:   63fdce1252f16032c9e1eb7244bb674ba4f84855
commit: bd5b16d6c88da451a46d068a25fafad8e83d14a6 [56/72] refperf: Allow decimal nanoseconds
config: m68k-allyesconfig (attached as .config)
compiler: m68k-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        git checkout bd5b16d6c88da451a46d068a25fafad8e83d14a6
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=m68k 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kbuild test robot <lkp@intel.com>

All errors (new ones prefixed by >>, old ones prefixed by <<):

m68k-linux-ld: kernel/rcu/refperf.o: in function `main_func':
>> refperf.c:(.text+0x762): undefined reference to `__umoddi3'
>> m68k-linux-ld: refperf.c:(.text+0x8f2): undefined reference to `__udivdi3'
m68k-linux-ld: refperf.c:(.text+0x97c): undefined reference to `__udivdi3'

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 54277 bytes --]

Re: [rcu:dev.2020.05.26a 56/72] refperf.c:undefined reference to `__umoddi3'

[Geert Uytterhoeven]

On Thu, May 28, 2020 at 5:26 AM kbuild test robot <lkp@intel.com> wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2020.05.26a
> head:   63fdce1252f16032c9e1eb7244bb674ba4f84855
> commit: bd5b16d6c88da451a46d068a25fafad8e83d14a6 [56/72] refperf: Allow decimal nanoseconds
> config: m68k-allyesconfig (attached as .config)
> compiler: m68k-linux-gcc (GCC) 9.3.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         git checkout bd5b16d6c88da451a46d068a25fafad8e83d14a6
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=m68k
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kbuild test robot <lkp@intel.com>
>
> All errors (new ones prefixed by >>, old ones prefixed by <<):
>
> m68k-linux-ld: kernel/rcu/refperf.o: in function `main_func':
> >> refperf.c:(.text+0x762): undefined reference to `__umoddi3'
> >> m68k-linux-ld: refperf.c:(.text+0x8f2): undefined reference to `__udivdi3'
> m68k-linux-ld: refperf.c:(.text+0x97c): undefined reference to `__udivdi3'

| --- a/kernel/rcu/refperf.c
| +++ b/kernel/rcu/refperf.c
| @@ -375,7 +375,7 @@ static int main_func(void *arg)
|                 if (torture_must_stop())
|                         goto end;
|
| -               reader_tasks[exp].result_avg =
process_durations(exp) / ((exp + 1) * loops);
| +               reader_tasks[exp].result_avg = 1000 *
process_durations(exp) / ((exp + 1) * loops);

div64_ul() for 64-by-unsigned-long division

|         }
|
|         // Print the average of all experiments
| @@ -386,7 +386,7 @@ static int main_func(void *arg)
|         strcat(buf, "Threads\tTime(ns)\n");
|
|         for (exp = 0; exp < nreaders; exp++) {
| -               sprintf(buf1, "%d\t%llu\n", exp + 1,
reader_tasks[exp].result_avg);
| +               sprintf(buf1, "%d\t%llu.%03d\n", exp + 1,
reader_tasks[exp].result_avg / 1000,
(int)(reader_tasks[exp].result_avg % 1000));

do_div() for 64-by-32 division/modulo

|                 strcat(buf, buf1);
|         }


Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [rcu:dev.2020.05.26a 56/72] refperf.c:undefined reference to `__umoddi3'

[Paul E. McKenney]

On Thu, May 28, 2020 at 09:04:38AM +0200, Geert Uytterhoeven wrote:
> On Thu, May 28, 2020 at 5:26 AM kbuild test robot <lkp@intel.com> wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2020.05.26a
> > head:   63fdce1252f16032c9e1eb7244bb674ba4f84855
> > commit: bd5b16d6c88da451a46d068a25fafad8e83d14a6 [56/72] refperf: Allow decimal nanoseconds
> > config: m68k-allyesconfig (attached as .config)
> > compiler: m68k-linux-gcc (GCC) 9.3.0
> > reproduce (this is a W=1 build):
> >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> >         chmod +x ~/bin/make.cross
> >         git checkout bd5b16d6c88da451a46d068a25fafad8e83d14a6
> >         # save the attached .config to linux build tree
> >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=m68k
> >
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kbuild test robot <lkp@intel.com>
> >
> > All errors (new ones prefixed by >>, old ones prefixed by <<):
> >
> > m68k-linux-ld: kernel/rcu/refperf.o: in function `main_func':
> > >> refperf.c:(.text+0x762): undefined reference to `__umoddi3'
> > >> m68k-linux-ld: refperf.c:(.text+0x8f2): undefined reference to `__udivdi3'
> > m68k-linux-ld: refperf.c:(.text+0x97c): undefined reference to `__udivdi3'
> 
> | --- a/kernel/rcu/refperf.c
> | +++ b/kernel/rcu/refperf.c
> | @@ -375,7 +375,7 @@ static int main_func(void *arg)
> |                 if (torture_must_stop())
> |                         goto end;
> |
> | -               reader_tasks[exp].result_avg =
> process_durations(exp) / ((exp + 1) * loops);
> | +               reader_tasks[exp].result_avg = 1000 *
> process_durations(exp) / ((exp + 1) * loops);
> 
> div64_ul() for 64-by-unsigned-long division

Ah, thank you for the explanation!

This is just a performance-test module intended for SMP systems, so
I don't see much point in making it work on m68k, which looks to be
UP-only.  But it is clearly useful to prevent the test bots from building
refperf on m68k.  So one approach would be for me to make its Kconfig
option depend on SMP.  Another would be to make it depend on 64BIT.
Still another would be to make it depend on !M68K.

I could potentially dump out the numbers in picoseconds, then
do the averaging and other division operations in userspace,
but that is strange enough to cause more trouble than it is worth.
(An rcu_read_lock()/rcu_read_unlock() pair takes -how- long???)  Though if
there was some point in running this on m68k, it might be worth it (with
"PICOSECONDS" in all caps or some such), but in this case it is not.
But this would probably require more data to be dumped to allow userspace
to do the operations, increasing the probability of lost printk()s.  :-/

Left to myself, I would take the easy way out and make this depend
on 64BIT.

But you must have run into this situation before.  Any thoughts?

							Thanx, Paul

> |         }
> |
> |         // Print the average of all experiments
> | @@ -386,7 +386,7 @@ static int main_func(void *arg)
> |         strcat(buf, "Threads\tTime(ns)\n");
> |
> |         for (exp = 0; exp < nreaders; exp++) {
> | -               sprintf(buf1, "%d\t%llu\n", exp + 1,
> reader_tasks[exp].result_avg);
> | +               sprintf(buf1, "%d\t%llu.%03d\n", exp + 1,
> reader_tasks[exp].result_avg / 1000,
> (int)(reader_tasks[exp].result_avg % 1000));
> 
> do_div() for 64-by-32 division/modulo
> 
> |                 strcat(buf, buf1);
> |         }
> 
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> -- 
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds

Re: [rcu:dev.2020.05.26a 56/72] refperf.c:undefined reference to `__umoddi3'

[Geert Uytterhoeven]

Hi Paul,

On Thu, May 28, 2020 at 3:51 PM Paul E. McKenney <paulmck@kernel.org> wrote:
> On Thu, May 28, 2020 at 09:04:38AM +0200, Geert Uytterhoeven wrote:
> > On Thu, May 28, 2020 at 5:26 AM kbuild test robot <lkp@intel.com> wrote:
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2020.05.26a
> > > head:   63fdce1252f16032c9e1eb7244bb674ba4f84855
> > > commit: bd5b16d6c88da451a46d068a25fafad8e83d14a6 [56/72] refperf: Allow decimal nanoseconds
> > > config: m68k-allyesconfig (attached as .config)
> > > compiler: m68k-linux-gcc (GCC) 9.3.0
> > > reproduce (this is a W=1 build):
> > >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > >         chmod +x ~/bin/make.cross
> > >         git checkout bd5b16d6c88da451a46d068a25fafad8e83d14a6
> > >         # save the attached .config to linux build tree
> > >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=m68k
> > >
> > > If you fix the issue, kindly add following tag as appropriate
> > > Reported-by: kbuild test robot <lkp@intel.com>
> > >
> > > All errors (new ones prefixed by >>, old ones prefixed by <<):
> > >
> > > m68k-linux-ld: kernel/rcu/refperf.o: in function `main_func':
> > > >> refperf.c:(.text+0x762): undefined reference to `__umoddi3'
> > > >> m68k-linux-ld: refperf.c:(.text+0x8f2): undefined reference to `__udivdi3'
> > > m68k-linux-ld: refperf.c:(.text+0x97c): undefined reference to `__udivdi3'
> >
> > | --- a/kernel/rcu/refperf.c
> > | +++ b/kernel/rcu/refperf.c
> > | @@ -375,7 +375,7 @@ static int main_func(void *arg)
> > |                 if (torture_must_stop())
> > |                         goto end;
> > |
> > | -               reader_tasks[exp].result_avg =
> > process_durations(exp) / ((exp + 1) * loops);
> > | +               reader_tasks[exp].result_avg = 1000 *
> > process_durations(exp) / ((exp + 1) * loops);
> >
> > div64_ul() for 64-by-unsigned-long division
>
> Ah, thank you for the explanation!
>
> This is just a performance-test module intended for SMP systems, so
> I don't see much point in making it work on m68k, which looks to be
> UP-only.  But it is clearly useful to prevent the test bots from building
> refperf on m68k.  So one approach would be for me to make its Kconfig
> option depend on SMP.  Another would be to make it depend on 64BIT.
> Still another would be to make it depend on !M68K.
>
> I could potentially dump out the numbers in picoseconds, then
> do the averaging and other division operations in userspace,
> but that is strange enough to cause more trouble than it is worth.
> (An rcu_read_lock()/rcu_read_unlock() pair takes -how- long???)  Though if
> there was some point in running this on m68k, it might be worth it (with
> "PICOSECONDS" in all caps or some such), but in this case it is not.
> But this would probably require more data to be dumped to allow userspace
> to do the operations, increasing the probability of lost printk()s.  :-/
>
> Left to myself, I would take the easy way out and make this depend
> on 64BIT.
>
> But you must have run into this situation before.  Any thoughts?

Oh, this is not just on m68k. I expect the build bots to start complaining
about other 32-bit platforms, too, like i386 and arm32 ;-)

While restricting this to 64BIT will fix the issue, are you sure people
on 32-bit SMP platforms don't want to run this code?

So I'd go for div64_ul() and do_div().

> > |         }
> > |
> > |         // Print the average of all experiments
> > | @@ -386,7 +386,7 @@ static int main_func(void *arg)
> > |         strcat(buf, "Threads\tTime(ns)\n");
> > |
> > |         for (exp = 0; exp < nreaders; exp++) {
> > | -               sprintf(buf1, "%d\t%llu\n", exp + 1,
> > reader_tasks[exp].result_avg);
> > | +               sprintf(buf1, "%d\t%llu.%03d\n", exp + 1,
> > reader_tasks[exp].result_avg / 1000,
> > (int)(reader_tasks[exp].result_avg % 1000));
> >
> > do_div() for 64-by-32 division/modulo

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [rcu:dev.2020.05.26a 56/72] refperf.c:undefined reference to `__umoddi3'

[Randy Dunlap]

On 5/28/20 8:31 AM, Geert Uytterhoeven wrote:
> Hi Paul,
> 
> On Thu, May 28, 2020 at 3:51 PM Paul E. McKenney <paulmck@kernel.org> wrote:
>> On Thu, May 28, 2020 at 09:04:38AM +0200, Geert Uytterhoeven wrote:
>>> On Thu, May 28, 2020 at 5:26 AM kbuild test robot <lkp@intel.com> wrote:
>>>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2020.05.26a
>>>> head:   63fdce1252f16032c9e1eb7244bb674ba4f84855
>>>> commit: bd5b16d6c88da451a46d068a25fafad8e83d14a6 [56/72] refperf: Allow decimal nanoseconds
>>>> config: m68k-allyesconfig (attached as .config)
>>>> compiler: m68k-linux-gcc (GCC) 9.3.0
>>>> reproduce (this is a W=1 build):
>>>>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>>>>         chmod +x ~/bin/make.cross
>>>>         git checkout bd5b16d6c88da451a46d068a25fafad8e83d14a6
>>>>         # save the attached .config to linux build tree
>>>>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=m68k
>>>>
>>>> If you fix the issue, kindly add following tag as appropriate
>>>> Reported-by: kbuild test robot <lkp@intel.com>
>>>>
>>>> All errors (new ones prefixed by >>, old ones prefixed by <<):
>>>>
>>>> m68k-linux-ld: kernel/rcu/refperf.o: in function `main_func':
>>>>>> refperf.c:(.text+0x762): undefined reference to `__umoddi3'
>>>>>> m68k-linux-ld: refperf.c:(.text+0x8f2): undefined reference to `__udivdi3'
>>>> m68k-linux-ld: refperf.c:(.text+0x97c): undefined reference to `__udivdi3'
>>>
>>> | --- a/kernel/rcu/refperf.c
>>> | +++ b/kernel/rcu/refperf.c
>>> | @@ -375,7 +375,7 @@ static int main_func(void *arg)
>>> |                 if (torture_must_stop())
>>> |                         goto end;
>>> |
>>> | -               reader_tasks[exp].result_avg =
>>> process_durations(exp) / ((exp + 1) * loops);
>>> | +               reader_tasks[exp].result_avg = 1000 *
>>> process_durations(exp) / ((exp + 1) * loops);
>>>
>>> div64_ul() for 64-by-unsigned-long division
>>
>> Ah, thank you for the explanation!
>>
>> This is just a performance-test module intended for SMP systems, so
>> I don't see much point in making it work on m68k, which looks to be
>> UP-only.  But it is clearly useful to prevent the test bots from building
>> refperf on m68k.  So one approach would be for me to make its Kconfig
>> option depend on SMP.  Another would be to make it depend on 64BIT.
>> Still another would be to make it depend on !M68K.
>>
>> I could potentially dump out the numbers in picoseconds, then
>> do the averaging and other division operations in userspace,
>> but that is strange enough to cause more trouble than it is worth.
>> (An rcu_read_lock()/rcu_read_unlock() pair takes -how- long???)  Though if
>> there was some point in running this on m68k, it might be worth it (with
>> "PICOSECONDS" in all caps or some such), but in this case it is not.
>> But this would probably require more data to be dumped to allow userspace
>> to do the operations, increasing the probability of lost printk()s.  :-/
>>
>> Left to myself, I would take the easy way out and make this depend
>> on 64BIT.
>>
>> But you must have run into this situation before.  Any thoughts?
> 
> Oh, this is not just on m68k. I expect the build bots to start complaining
> about other 32-bit platforms, too, like i386 and arm32 ;-)

Yes, I was just about to report it for/on i386.


> While restricting this to 64BIT will fix the issue, are you sure people
> on 32-bit SMP platforms don't want to run this code?
> 
> So I'd go for div64_ul() and do_div().
> 
>>> |         }
>>> |
>>> |         // Print the average of all experiments
>>> | @@ -386,7 +386,7 @@ static int main_func(void *arg)
>>> |         strcat(buf, "Threads\tTime(ns)\n");
>>> |
>>> |         for (exp = 0; exp < nreaders; exp++) {
>>> | -               sprintf(buf1, "%d\t%llu\n", exp + 1,
>>> reader_tasks[exp].result_avg);
>>> | +               sprintf(buf1, "%d\t%llu.%03d\n", exp + 1,
>>> reader_tasks[exp].result_avg / 1000,
>>> (int)(reader_tasks[exp].result_avg % 1000));
>>>
>>> do_div() for 64-by-32 division/modulo
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 

thanks.
-- 
~Randy

Re: [rcu:dev.2020.05.26a 56/72] refperf.c:undefined reference to `__umoddi3'

[Paul E. McKenney]

On Thu, May 28, 2020 at 05:31:33PM +0200, Geert Uytterhoeven wrote:
> Hi Paul,
> 
> On Thu, May 28, 2020 at 3:51 PM Paul E. McKenney <paulmck@kernel.org> wrote:
> > On Thu, May 28, 2020 at 09:04:38AM +0200, Geert Uytterhoeven wrote:
> > > On Thu, May 28, 2020 at 5:26 AM kbuild test robot <lkp@intel.com> wrote:
> > > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2020.05.26a
> > > > head:   63fdce1252f16032c9e1eb7244bb674ba4f84855
> > > > commit: bd5b16d6c88da451a46d068a25fafad8e83d14a6 [56/72] refperf: Allow decimal nanoseconds
> > > > config: m68k-allyesconfig (attached as .config)
> > > > compiler: m68k-linux-gcc (GCC) 9.3.0
> > > > reproduce (this is a W=1 build):
> > > >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > > >         chmod +x ~/bin/make.cross
> > > >         git checkout bd5b16d6c88da451a46d068a25fafad8e83d14a6
> > > >         # save the attached .config to linux build tree
> > > >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=m68k
> > > >
> > > > If you fix the issue, kindly add following tag as appropriate
> > > > Reported-by: kbuild test robot <lkp@intel.com>
> > > >
> > > > All errors (new ones prefixed by >>, old ones prefixed by <<):
> > > >
> > > > m68k-linux-ld: kernel/rcu/refperf.o: in function `main_func':
> > > > >> refperf.c:(.text+0x762): undefined reference to `__umoddi3'
> > > > >> m68k-linux-ld: refperf.c:(.text+0x8f2): undefined reference to `__udivdi3'
> > > > m68k-linux-ld: refperf.c:(.text+0x97c): undefined reference to `__udivdi3'
> > >
> > > | --- a/kernel/rcu/refperf.c
> > > | +++ b/kernel/rcu/refperf.c
> > > | @@ -375,7 +375,7 @@ static int main_func(void *arg)
> > > |                 if (torture_must_stop())
> > > |                         goto end;
> > > |
> > > | -               reader_tasks[exp].result_avg =
> > > process_durations(exp) / ((exp + 1) * loops);
> > > | +               reader_tasks[exp].result_avg = 1000 *
> > > process_durations(exp) / ((exp + 1) * loops);
> > >
> > > div64_ul() for 64-by-unsigned-long division
> >
> > Ah, thank you for the explanation!
> >
> > This is just a performance-test module intended for SMP systems, so
> > I don't see much point in making it work on m68k, which looks to be
> > UP-only.  But it is clearly useful to prevent the test bots from building
> > refperf on m68k.  So one approach would be for me to make its Kconfig
> > option depend on SMP.  Another would be to make it depend on 64BIT.
> > Still another would be to make it depend on !M68K.
> >
> > I could potentially dump out the numbers in picoseconds, then
> > do the averaging and other division operations in userspace,
> > but that is strange enough to cause more trouble than it is worth.
> > (An rcu_read_lock()/rcu_read_unlock() pair takes -how- long???)  Though if
> > there was some point in running this on m68k, it might be worth it (with
> > "PICOSECONDS" in all caps or some such), but in this case it is not.
> > But this would probably require more data to be dumped to allow userspace
> > to do the operations, increasing the probability of lost printk()s.  :-/
> >
> > Left to myself, I would take the easy way out and make this depend
> > on 64BIT.
> >
> > But you must have run into this situation before.  Any thoughts?
> 
> Oh, this is not just on m68k. I expect the build bots to start complaining
> about other 32-bit platforms, too, like i386 and arm32 ;-)
> 
> While restricting this to 64BIT will fix the issue, are you sure people
> on 32-bit SMP platforms don't want to run this code?

In the unlikely event that they do, we can go from there.

> So I'd go for div64_ul() and do_div().

OK, I will bite...  Plus my feeble web search failed to satisfy my
idle curiosity on this point.  ;-)

Why can't these 32-bit SMP platforms supply the API that the compiler
expects, so that normal C-language arithmetic just works?

							Thanx, Paul

> > > |         }
> > > |
> > > |         // Print the average of all experiments
> > > | @@ -386,7 +386,7 @@ static int main_func(void *arg)
> > > |         strcat(buf, "Threads\tTime(ns)\n");
> > > |
> > > |         for (exp = 0; exp < nreaders; exp++) {
> > > | -               sprintf(buf1, "%d\t%llu\n", exp + 1,
> > > reader_tasks[exp].result_avg);
> > > | +               sprintf(buf1, "%d\t%llu.%03d\n", exp + 1,
> > > reader_tasks[exp].result_avg / 1000,
> > > (int)(reader_tasks[exp].result_avg % 1000));
> > >
> > > do_div() for 64-by-32 division/modulo
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> -- 
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds

Re: [rcu:dev.2020.05.26a 56/72] refperf.c:undefined reference to `__umoddi3'

[Geert Uytterhoeven]

Hi Paul,

On Thu, May 28, 2020 at 6:28 PM Paul E. McKenney <paulmck@kernel.org> wrote:
> On Thu, May 28, 2020 at 05:31:33PM +0200, Geert Uytterhoeven wrote:
> > On Thu, May 28, 2020 at 3:51 PM Paul E. McKenney <paulmck@kernel.org> wrote:
> > > On Thu, May 28, 2020 at 09:04:38AM +0200, Geert Uytterhoeven wrote:
> > > > On Thu, May 28, 2020 at 5:26 AM kbuild test robot <lkp@intel.com> wrote:
> > > > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2020.05.26a
> > > > > head:   63fdce1252f16032c9e1eb7244bb674ba4f84855
> > > > > commit: bd5b16d6c88da451a46d068a25fafad8e83d14a6 [56/72] refperf: Allow decimal nanoseconds
> > > > > config: m68k-allyesconfig (attached as .config)
> > > > > compiler: m68k-linux-gcc (GCC) 9.3.0
> > > > > reproduce (this is a W=1 build):
> > > > >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > > > >         chmod +x ~/bin/make.cross
> > > > >         git checkout bd5b16d6c88da451a46d068a25fafad8e83d14a6
> > > > >         # save the attached .config to linux build tree
> > > > >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=m68k
> > > > >
> > > > > If you fix the issue, kindly add following tag as appropriate
> > > > > Reported-by: kbuild test robot <lkp@intel.com>
> > > > >
> > > > > All errors (new ones prefixed by >>, old ones prefixed by <<):
> > > > >
> > > > > m68k-linux-ld: kernel/rcu/refperf.o: in function `main_func':
> > > > > >> refperf.c:(.text+0x762): undefined reference to `__umoddi3'
> > > > > >> m68k-linux-ld: refperf.c:(.text+0x8f2): undefined reference to `__udivdi3'
> > > > > m68k-linux-ld: refperf.c:(.text+0x97c): undefined reference to `__udivdi3'
> > > >
> > > > | --- a/kernel/rcu/refperf.c
> > > > | +++ b/kernel/rcu/refperf.c
> > > > | @@ -375,7 +375,7 @@ static int main_func(void *arg)
> > > > |                 if (torture_must_stop())
> > > > |                         goto end;
> > > > |
> > > > | -               reader_tasks[exp].result_avg =
> > > > process_durations(exp) / ((exp + 1) * loops);
> > > > | +               reader_tasks[exp].result_avg = 1000 *
> > > > process_durations(exp) / ((exp + 1) * loops);
> > > >
> > > > div64_ul() for 64-by-unsigned-long division
> > >
> > > Ah, thank you for the explanation!
> > >
> > > This is just a performance-test module intended for SMP systems, so
> > > I don't see much point in making it work on m68k, which looks to be
> > > UP-only.  But it is clearly useful to prevent the test bots from building
> > > refperf on m68k.  So one approach would be for me to make its Kconfig
> > > option depend on SMP.  Another would be to make it depend on 64BIT.
> > > Still another would be to make it depend on !M68K.
> > >
> > > I could potentially dump out the numbers in picoseconds, then
> > > do the averaging and other division operations in userspace,
> > > but that is strange enough to cause more trouble than it is worth.
> > > (An rcu_read_lock()/rcu_read_unlock() pair takes -how- long???)  Though if
> > > there was some point in running this on m68k, it might be worth it (with
> > > "PICOSECONDS" in all caps or some such), but in this case it is not.
> > > But this would probably require more data to be dumped to allow userspace
> > > to do the operations, increasing the probability of lost printk()s.  :-/
> > >
> > > Left to myself, I would take the easy way out and make this depend
> > > on 64BIT.
> > >
> > > But you must have run into this situation before.  Any thoughts?
> >
> > Oh, this is not just on m68k. I expect the build bots to start complaining
> > about other 32-bit platforms, too, like i386 and arm32 ;-)
> >
> > While restricting this to 64BIT will fix the issue, are you sure people
> > on 32-bit SMP platforms don't want to run this code?
>
> In the unlikely event that they do, we can go from there.
>
> > So I'd go for div64_ul() and do_div().
>
> OK, I will bite...  Plus my feeble web search failed to satisfy my
> idle curiosity on this point.  ;-)
>
> Why can't these 32-bit SMP platforms supply the API that the compiler
> expects, so that normal C-language arithmetic just works?

This is done on purpose, to avoid people accidentally introducing expensive
64-bit divisions on 32-bit platforms.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [rcu:dev.2020.05.26a 56/72] refperf.c:undefined reference to `__umoddi3'

[Paul E. McKenney]

On Thu, May 28, 2020 at 07:25:01PM +0200, Geert Uytterhoeven wrote:
> Hi Paul,
> 
> On Thu, May 28, 2020 at 6:28 PM Paul E. McKenney <paulmck@kernel.org> wrote:
> > On Thu, May 28, 2020 at 05:31:33PM +0200, Geert Uytterhoeven wrote:
> > > On Thu, May 28, 2020 at 3:51 PM Paul E. McKenney <paulmck@kernel.org> wrote:
> > > > On Thu, May 28, 2020 at 09:04:38AM +0200, Geert Uytterhoeven wrote:
> > > > > On Thu, May 28, 2020 at 5:26 AM kbuild test robot <lkp@intel.com> wrote:
> > > > > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2020.05.26a
> > > > > > head:   63fdce1252f16032c9e1eb7244bb674ba4f84855
> > > > > > commit: bd5b16d6c88da451a46d068a25fafad8e83d14a6 [56/72] refperf: Allow decimal nanoseconds
> > > > > > config: m68k-allyesconfig (attached as .config)
> > > > > > compiler: m68k-linux-gcc (GCC) 9.3.0
> > > > > > reproduce (this is a W=1 build):
> > > > > >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > > > > >         chmod +x ~/bin/make.cross
> > > > > >         git checkout bd5b16d6c88da451a46d068a25fafad8e83d14a6
> > > > > >         # save the attached .config to linux build tree
> > > > > >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=m68k
> > > > > >
> > > > > > If you fix the issue, kindly add following tag as appropriate
> > > > > > Reported-by: kbuild test robot <lkp@intel.com>
> > > > > >
> > > > > > All errors (new ones prefixed by >>, old ones prefixed by <<):
> > > > > >
> > > > > > m68k-linux-ld: kernel/rcu/refperf.o: in function `main_func':
> > > > > > >> refperf.c:(.text+0x762): undefined reference to `__umoddi3'
> > > > > > >> m68k-linux-ld: refperf.c:(.text+0x8f2): undefined reference to `__udivdi3'
> > > > > > m68k-linux-ld: refperf.c:(.text+0x97c): undefined reference to `__udivdi3'
> > > > >
> > > > > | --- a/kernel/rcu/refperf.c
> > > > > | +++ b/kernel/rcu/refperf.c
> > > > > | @@ -375,7 +375,7 @@ static int main_func(void *arg)
> > > > > |                 if (torture_must_stop())
> > > > > |                         goto end;
> > > > > |
> > > > > | -               reader_tasks[exp].result_avg =
> > > > > process_durations(exp) / ((exp + 1) * loops);
> > > > > | +               reader_tasks[exp].result_avg = 1000 *
> > > > > process_durations(exp) / ((exp + 1) * loops);
> > > > >
> > > > > div64_ul() for 64-by-unsigned-long division
> > > >
> > > > Ah, thank you for the explanation!
> > > >
> > > > This is just a performance-test module intended for SMP systems, so
> > > > I don't see much point in making it work on m68k, which looks to be
> > > > UP-only.  But it is clearly useful to prevent the test bots from building
> > > > refperf on m68k.  So one approach would be for me to make its Kconfig
> > > > option depend on SMP.  Another would be to make it depend on 64BIT.
> > > > Still another would be to make it depend on !M68K.
> > > >
> > > > I could potentially dump out the numbers in picoseconds, then
> > > > do the averaging and other division operations in userspace,
> > > > but that is strange enough to cause more trouble than it is worth.
> > > > (An rcu_read_lock()/rcu_read_unlock() pair takes -how- long???)  Though if
> > > > there was some point in running this on m68k, it might be worth it (with
> > > > "PICOSECONDS" in all caps or some such), but in this case it is not.
> > > > But this would probably require more data to be dumped to allow userspace
> > > > to do the operations, increasing the probability of lost printk()s.  :-/
> > > >
> > > > Left to myself, I would take the easy way out and make this depend
> > > > on 64BIT.
> > > >
> > > > But you must have run into this situation before.  Any thoughts?
> > >
> > > Oh, this is not just on m68k. I expect the build bots to start complaining
> > > about other 32-bit platforms, too, like i386 and arm32 ;-)
> > >
> > > While restricting this to 64BIT will fix the issue, are you sure people
> > > on 32-bit SMP platforms don't want to run this code?
> >
> > In the unlikely event that they do, we can go from there.
> >
> > > So I'd go for div64_ul() and do_div().
> >
> > OK, I will bite...  Plus my feeble web search failed to satisfy my
> > idle curiosity on this point.  ;-)
> >
> > Why can't these 32-bit SMP platforms supply the API that the compiler
> > expects, so that normal C-language arithmetic just works?
> 
> This is done on purpose, to avoid people accidentally introducing expensive
> 64-bit divisions on 32-bit platforms.

Fair enough, and thank you for the explanation!  Though in this case,
these divisions are nowhere near anything even vaguely resembling a
fastpath.  They instead happen at the end of the run, while doing output.

So I am restricting to 64BIT for the time being.  Yeah, I know, lazy of
me.  ;-)

							Thanx, Paul