Re: [PATCH v3 sched_ext/for-6.13] sched_ext: Do not enable LLC/NUMA optimizations when domains overlap

Re: [PATCH v3 sched_ext/for-6.13] sched_ext: Do not enable LLC/NUMA optimizations when domains overlap

[Nathan Chancellor]

Hi Andrea,

On Fri, Nov 08, 2024 at 01:01:36AM +0100, Andrea Righi wrote:
...
> +	/*
> +	 * Enable NUMA optimization only when there are multiple NUMA domains
> +	 * among the online CPUs and the NUMA domains don't perfectly overlaps
> +	 * with the LLC domains.
> +	 *
> +	 * If all CPUs belong to the same NUMA node and the same LLC domain,
> +	 * enabling both NUMA and LLC optimizations is unnecessary, as checking
> +	 * for an idle CPU in the same domain twice is redundant.
> +	 */
> +	cpus = cpumask_of_node(cpu_to_node(cpu));
> +	if ((cpumask_weight(cpus) < num_online_cpus()) & llc_numa_mismatch())
> +		enable_numa = true;

With this hunk in next-20241108, I am seeing a clang warning (or error
since CONFIG_WERROR=y):

  In file included from kernel/sched/build_policy.c:63:
  kernel/sched/ext.c:3252:6: error: use of bitwise '&' with boolean operands [-Werror,-Wbitwise-instead-of-logical]
   3252 |         if ((cpumask_weight(cpus) < num_online_cpus()) & llc_numa_mismatch())
        |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        |                                                        &&
  kernel/sched/ext.c:3252:6: note: cast one or both operands to int to silence this warning
  1 error generated.

Was use of a bitwise AND here intentional (i.e., should
llc_num_mismatch() always be called regardless of the outcome of the
first condition) or can it be switched to a logical AND to silence the
warning? I do not mind sending a patch but I did not want to be wrong
off bat. If there is some other better solution that I am not seeing,
please feel free to send a patch with this as just a report.

Cheers,
Nathan

Re: [PATCH v3 sched_ext/for-6.13] sched_ext: Do not enable LLC/NUMA optimizations when domains overlap

[Tejun Heo]

On Fri, Nov 08, 2024 at 11:17:53AM -0700, Nathan Chancellor wrote:
> Hi Andrea,
> 
> On Fri, Nov 08, 2024 at 01:01:36AM +0100, Andrea Righi wrote:
> ...
> > +	/*
> > +	 * Enable NUMA optimization only when there are multiple NUMA domains
> > +	 * among the online CPUs and the NUMA domains don't perfectly overlaps
> > +	 * with the LLC domains.
> > +	 *
> > +	 * If all CPUs belong to the same NUMA node and the same LLC domain,
> > +	 * enabling both NUMA and LLC optimizations is unnecessary, as checking
> > +	 * for an idle CPU in the same domain twice is redundant.
> > +	 */
> > +	cpus = cpumask_of_node(cpu_to_node(cpu));
> > +	if ((cpumask_weight(cpus) < num_online_cpus()) & llc_numa_mismatch())
> > +		enable_numa = true;
> 
> With this hunk in next-20241108, I am seeing a clang warning (or error
> since CONFIG_WERROR=y):
> 
>   In file included from kernel/sched/build_policy.c:63:
>   kernel/sched/ext.c:3252:6: error: use of bitwise '&' with boolean operands [-Werror,-Wbitwise-instead-of-logical]
>    3252 |         if ((cpumask_weight(cpus) < num_online_cpus()) & llc_numa_mismatch())
>         |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>         |                                                        &&
>   kernel/sched/ext.c:3252:6: note: cast one or both operands to int to silence this warning
>   1 error generated.
> 
> Was use of a bitwise AND here intentional (i.e., should
> llc_num_mismatch() always be called regardless of the outcome of the
> first condition) or can it be switched to a logical AND to silence the
> warning? I do not mind sending a patch but I did not want to be wrong
> off bat. If there is some other better solution that I am not seeing,
> please feel free to send a patch with this as just a report.

Oops, that looks like a mistake. I don't see why it can't be &&.

Thanks.

-- 
tejun

Re: [PATCH v3 sched_ext/for-6.13] sched_ext: Do not enable LLC/NUMA optimizations when domains overlap

[Andrea Righi]

On Fri, Nov 08, 2024 at 08:54:33AM -1000, Tejun Heo wrote:
> On Fri, Nov 08, 2024 at 11:17:53AM -0700, Nathan Chancellor wrote:
> > Hi Andrea,
> >
> > On Fri, Nov 08, 2024 at 01:01:36AM +0100, Andrea Righi wrote:
> > ...
> > > +   /*
> > > +    * Enable NUMA optimization only when there are multiple NUMA domains
> > > +    * among the online CPUs and the NUMA domains don't perfectly overlaps
> > > +    * with the LLC domains.
> > > +    *
> > > +    * If all CPUs belong to the same NUMA node and the same LLC domain,
> > > +    * enabling both NUMA and LLC optimizations is unnecessary, as checking
> > > +    * for an idle CPU in the same domain twice is redundant.
> > > +    */
> > > +   cpus = cpumask_of_node(cpu_to_node(cpu));
> > > +   if ((cpumask_weight(cpus) < num_online_cpus()) & llc_numa_mismatch())
> > > +           enable_numa = true;
> >
> > With this hunk in next-20241108, I am seeing a clang warning (or error
> > since CONFIG_WERROR=y):
> >
> >   In file included from kernel/sched/build_policy.c:63:
> >   kernel/sched/ext.c:3252:6: error: use of bitwise '&' with boolean operands [-Werror,-Wbitwise-instead-of-logical]
> >    3252 |         if ((cpumask_weight(cpus) < num_online_cpus()) & llc_numa_mismatch())
> >         |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >         |                                                        &&
> >   kernel/sched/ext.c:3252:6: note: cast one or both operands to int to silence this warning
> >   1 error generated.
> >
> > Was use of a bitwise AND here intentional (i.e., should
> > llc_num_mismatch() always be called regardless of the outcome of the
> > first condition) or can it be switched to a logical AND to silence the
> > warning? I do not mind sending a patch but I did not want to be wrong
> > off bat. If there is some other better solution that I am not seeing,
> > please feel free to send a patch with this as just a report.
> 
> Oops, that looks like a mistake. I don't see why it can't be &&.

Sorry, this is a mistake, it definitely needs to be &&.

Do you want me to send a fix on top of this one or a v4?

Thanks,
-Andrea

Re: [PATCH v3 sched_ext/for-6.13] sched_ext: Do not enable LLC/NUMA optimizations when domains overlap

[Tejun Heo]

On Fri, Nov 08, 2024 at 08:39:15PM +0100, Andrea Righi wrote:
> Sorry, this is a mistake, it definitely needs to be &&.
> 
> Do you want me to send a fix on top of this one or a v4?

An incremental fix patch would be great.

Thanks.

-- 
tejun

Re: [PATCH v3 sched_ext/for-6.13] sched_ext: Do not enable LLC/NUMA optimizations when domains overlap

[Andrea Righi]

On Fri, Nov 08, 2024 at 09:42:44AM -1000, Tejun Heo wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Fri, Nov 08, 2024 at 08:39:15PM +0100, Andrea Righi wrote:
> > Sorry, this is a mistake, it definitely needs to be &&.
> >
> > Do you want me to send a fix on top of this one or a v4?
> 
> An incremental fix patch would be great.
> 
> Thanks.

Sent. Thanks Nathan for noticing it!

-Andrea