Messages in this thread | | | Subject | Re: [Patch v4 1/3] lib: Restrict cpumask_local_spread to houskeeping CPUs | From | Robin Murphy <> | Date | Wed, 27 Jan 2021 11:57:16 +0000 |
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Hi,
On 2020-06-25 23:34, Nitesh Narayan Lal wrote: > From: Alex Belits <abelits@marvell.com> > > The current implementation of cpumask_local_spread() does not respect the > isolated CPUs, i.e., even if a CPU has been isolated for Real-Time task, > it will return it to the caller for pinning of its IRQ threads. Having > these unwanted IRQ threads on an isolated CPU adds up to a latency > overhead. > > Restrict the CPUs that are returned for spreading IRQs only to the > available housekeeping CPUs. > > Signed-off-by: Alex Belits <abelits@marvell.com> > Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com> > --- > lib/cpumask.c | 16 +++++++++++----- > 1 file changed, 11 insertions(+), 5 deletions(-) > > diff --git a/lib/cpumask.c b/lib/cpumask.c > index fb22fb266f93..85da6ab4fbb5 100644 > --- a/lib/cpumask.c > +++ b/lib/cpumask.c > @@ -6,6 +6,7 @@ > #include <linux/export.h> > #include <linux/memblock.h> > #include <linux/numa.h> > +#include <linux/sched/isolation.h> > > /** > * cpumask_next - get the next cpu in a cpumask > @@ -205,22 +206,27 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask) > */ > unsigned int cpumask_local_spread(unsigned int i, int node) > { > - int cpu; > + int cpu, hk_flags; > + const struct cpumask *mask; > > + hk_flags = HK_FLAG_DOMAIN | HK_FLAG_MANAGED_IRQ; > + mask = housekeeping_cpumask(hk_flags);
AFAICS, this generally resolves to something based on cpu_possible_mask rather than cpu_online_mask as before, so could now potentially return an offline CPU. Was that an intentional change?
I was just looking at the current code since I had the rare presence of mind to check if something suitable already existed before I start open-coding "any online CPU, but local node preferred" logic for handling IRQ affinity in a driver - cpumask_local_spread() appears to be almost what I want (if a bit more heavyweight), if only it would actually guarantee an online CPU as the kerneldoc claims :(
Robin.
> /* Wrap: we always want a cpu. */ > - i %= num_online_cpus(); > + i %= cpumask_weight(mask); > > if (node == NUMA_NO_NODE) { > - for_each_cpu(cpu, cpu_online_mask) > + for_each_cpu(cpu, mask) { > if (i-- == 0) > return cpu; > + } > } else { > /* NUMA first. */ > - for_each_cpu_and(cpu, cpumask_of_node(node), cpu_online_mask) > + for_each_cpu_and(cpu, cpumask_of_node(node), mask) { > if (i-- == 0) > return cpu; > + } > > - for_each_cpu(cpu, cpu_online_mask) { > + for_each_cpu(cpu, mask) { > /* Skip NUMA nodes, done above. */ > if (cpumask_test_cpu(cpu, cpumask_of_node(node))) > continue; >
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