Re: [PATCH v2 1/4] sched/rt: Optimize cpupri_vec layout to mitigate cache line contention

[Peter Zijlstra]

On Tue, Mar 24, 2026 at 09:36:14AM +0000, Deng, Pan wrote:

> Regarding this patch, yes, using cacheline aligned could increase potential
> memory usage.
> After internal discussion, we are thinking of an alternative method to
> mitigate the waste of memory usage, that is, using kmalloc() to allocate
> count in a different memory space rather than placing the count and
> cpumask together in this structure. The rationale is that, writing to
> address pointed by the counter and reading the address from cpumask
> is isolated in different memory space which could reduce the ratio of
> cache false sharing, besides, kmalloc() based on slub/slab could place
> the objects in different cache lines to reduce the cache contention.
> The drawback of dynamic allocation counter is that, we have to maintain
> the life cycle of the counters.
> Could you please advise if sticking with current cache_align attribute
> method or using kmalloc() is preferred?

Well, you'd have to allocate a full cacheline anyway. If you allocate N
4 byte (counter) objects, there's a fair chance they end up in the same
cacheline (its a SLAB after all) and then you're back to having a ton of
false sharing.

Anyway, for you specific workload, why isn't partitioning a viable
solution? It would not need any kernel modifications and would get rid
of the contention entirely.