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Mon, 5 Aug 2024 14:53:51 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id g4cVOH/nsGaMVQAAD6G6ig (envelope-from ); Mon, 05 Aug 2024 14:53:51 +0000 Message-ID: <00914d25-f0ae-4b00-9608-2457821c071c@suse.cz> Date: Mon, 5 Aug 2024 16:53:51 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 12/20] kthread: Implement preferred affinity Content-Language: en-US To: Frederic Weisbecker Cc: LKML , Andrew Morton , Kees Cook , Peter Zijlstra , Thomas Gleixner , Michal Hocko , linux-mm@kvack.org, "Paul E. McKenney" , Neeraj Upadhyay , Joel Fernandes , Boqun Feng , Zqiang , rcu@vger.kernel.org References: <20240726215701.19459-1-frederic@kernel.org> <20240726215701.19459-13-frederic@kernel.org> <4e9d1f6d-9cd8-493c-9440-b46a99f1c8af@suse.cz> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: nmbgs1aenmxe45amgwk1zpp3kgctmieu X-Rspamd-Queue-Id: E0A83140006 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1722869633-506661 X-HE-Meta: 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 jaDAdmUd ZUrvIxR/LqYmh/R/iXch4L3ErGHm+kxSc94zpzqw6UQIn2DQrS3WvWsVIf57BhcBZBPF2KlFDqyiWpuibPFzzgHkRpB5WIXdkdr6tEJtKPJ9xlqYA2YCdNusHxE9KvcF8FXYNjMmiw9i+dHi5+GV1SzLlMqY1x3HXoQSb90Ugmip/HnmHUpJAgdQrwsX98ud+p9/WDU/qZOgToazDHMz/QLTcBZPrCd8pCC7m1KHDKgjYxLWjKOCDGBH/46ViMFwJx7Z9t2q4wiu4KzWUQS54jLgPvJ0Bm+DfSNKAjJx3LJ35dJ8KS+0pVHvXGL2w6O1e6RG3b73r0ntZJBZRX5BCcUDUqnE348X/WtOEtikZ3sivteg= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/5/24 16:28, Frederic Weisbecker wrote: > Le Tue, Jul 30, 2024 at 05:49:51PM +0200, Vlastimil Babka a écrit : >> Acked-by: Vlastimil Babka >> >> Nit: >> >> > +int kthread_affine_preferred(struct task_struct *p, const struct cpumask *mask) >> > +{ >> > + struct kthread *kthread = to_kthread(p); >> > + cpumask_var_t affinity; >> > + unsigned long flags; >> > + int ret; >> > + >> > + if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE) || kthread->started) { >> > + WARN_ON(1); >> > + return -EINVAL; >> > + } >> > + >> >> Should we also fail if kthread->preferred_affinity already exist? In >> case somebody calls this twice. > > Good point! > >> >> Also for some of the use cases (kswapd, kcompactd) it would make sense >> to be able to add cpus of a node as they are onlined. Which seems we >> didn't do, except some corner case handling in kcompactd, but maybe we >> should? I wonder if the current implementation of onlining a completely >> new node with cpus does the right thing as a result of the individual >> onlining operations, or we end up with being affined to a single cpu (or >> none). >> >> But that would need some kind of kthread_affine_preferred_update() >> implementation? > > So you mean that the "for_each_node_state()" loop in kcompactd doesn't > handle all possible nodes but only those online when it's called? Or > am I confused? If you mean the loop in kcompactd_init() then indeed, but we also have a hook in online_pages() to start new threads on newly onlined nodes, so that's not a problem. The problem (I think) I see is cpumask_of_node(pgdat->node_id) is a snapshot of cpus running on the NUMA node the time, and is never updated later as new cpus might be brought up. kcompactd_cpu_online() does try to update that when cpus are onlined (in a clumsy way), there was nothing like that for kswapd and after your series this update is also removed for kcompactd. > If all users of preferred affinity were to use NUMA nodes, it could be > a good idea to do a flavour of kernel/smpboot.c which would handle > per-node kthreads instead of per-cpu kthreads. I initially thought > about that. It would have handled all the lifecycle of those kthreads, > including creation, against hotplug. Unfortunately RCU doesn't rely on > per-NUMA nodes but rather use its own tree. > > If there be more users of real per NUMA nodes kthreads than kswapd and > kcompactd, of course that would be much worth considering. Yeah it's not that compelling, but a way to update the preferred affine mask in response to cpu hotplug events, that kswapd and kcompactd could use, would be sufficient. And maybe more widely useful. I guess there could be a callback defined for kthread to provide a new preferred_affinity, that you'd call from kthreads_hotplug_update() ? And kcompactd and kswapd could both use the same callback that interprets kthread_data() as pgdat and fetches a new cpumask of it? > Thanks.