Re: [PATCH v3 sched_ext/for-6.13] sched_ext: Do not enable LLC/NUMA optimizations when domains overlap
From: Tejun Heo
Date: Fri Nov 08 2024 - 13:54:45 EST
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