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Wed, 29 Oct 2025 13:20:12 +0000 Message-ID: <253f00cc-2bea-43b6-aca3-96105014c4be@intel.com> Date: Wed, 29 Oct 2025 21:19:54 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 10/19] sched/fair: Prioritize tasks preferring destination LLC during balancing To: Aaron Lu CC: Tim Chen , Peter Zijlstra , Ingo Molnar , K Prateek Nayak , "Gautham R . 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>>>> } >>>> + >>>> +/* >>>> + * Do LLC balance on sched group that contains LLC, and have tasks preferring >>>> + * to run on LLC in idle dst_cpu. >>>> + */ >>>> +static inline bool llc_balance(struct lb_env *env, struct sg_lb_stats *sgs, >>>> + struct sched_group *group) >>>> +{ >>>> + struct sched_domain *child = env->sd->child; >>>> + int llc; >>>> + >>>> + if (!sched_cache_enabled()) >>>> + return false; >>>> + >>>> + if (env->sd->flags & SD_SHARE_LLC) >>>> + return false; >>>> + >>>> + /* only care about task migration among LLCs */ >>>> + if (child && !(child->flags & SD_SHARE_LLC)) >>>> + return false; >>>> + >>>> + llc = llc_idx(env->dst_cpu); >>>> + if (sgs->nr_pref_llc[llc] > 0 && >>>> + can_migrate_llc(env->src_cpu, env->dst_cpu, 0, true) == mig_llc) >>> >>> llc_balance() is called from update_sg_lb_stats() and at that time, >>> env->src_cpu is not determined yet so should not be used here? >>> >> >> You are right, I think we should check the candidate group's first >> CPU rather than the env->src_cpu. Will fix it in the next version. > > Looks like can_migrate_llc() doesn't care an exact cpu but any cpu in the > same LLC should do, so either the candidate group's first cpu or any > other cpus in that group should make no difference. > Yes, actually the cache aware is based on LLC rather than CPU. It was a historic reason that the original proposal was based on CPU in the wakeup path. > It might be more intuitive to prototype can_migrate_llc() with sd_shared > as param than using cpu, just a thought. I understand your concern, will think about this. thanks, Chenyu