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Wed, 11 Feb 2026 16:59:13 +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 NYLxHmG1jGnoUgAAD6G6ig (envelope-from ); Wed, 11 Feb 2026 16:59:13 +0000 Message-ID: <40b42d83-3667-4489-818f-a01e1114d6b0@suse.cz> Date: Wed, 11 Feb 2026 17:59:13 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/4] Introduce QPW for per-cpu operations Content-Language: en-US To: Marcelo Tosatti , Michal Hocko Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Johannes Weiner , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Leonardo Bras , Thomas Gleixner , Waiman Long , Boqun Feng , Frederic Weisbecker References: <20260206143430.021026873@redhat.com> 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+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Stat-Signature: qsz98k9sh6dfwh3oqp1697jbywkfa84p X-Rspam-User: X-Rspamd-Queue-Id: A8DF31C0010 X-HE-Tag: 1770829155-116013 X-HE-Meta: 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 Bffxu/sa sm64CZF4gHTXlA8DuPyoVqjnyImSJU1gJfaZo+4TOXMezTImlNIqHnRpgQmzG5yQeDl+lKwJ/59/8h37nTKnf8IM58k1XgOt5xA77H6cJQEgK4RlqO5JqDJApSntZl9WwaPC3N5v8Tzl2BF9CVe/pLr1mNwDwDF/nYrltBBhM0GE0Zee5++pThg2YFCI3rIgcSOGPypSPzGTH3QbipFv9apivJwUWz4K46yXJ0QXb56oZfb362ptziZMtrCSUwySzvFJAWmMOqcKzndO1h4oA1XQ5iJ3qhdvoVyfHjbZhLbq5Pc2+QyFdQGCKZ0tCZNgI8FVFXEwroHbZKt6f8nu8jmzep45dyx9fnsgIWSsMzOmhyYcLGn2CRZYhvJ7lPH1pEmatWFUyqDDaIIwabJ5UYSuzzA== 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 2/11/26 17:50, Marcelo Tosatti wrote: > On Wed, Feb 11, 2026 at 05:38:47PM +0100, Michal Hocko wrote: >> On Wed 11-02-26 09:01:12, Marcelo Tosatti wrote: >> > On Tue, Feb 10, 2026 at 03:01:10PM +0100, Michal Hocko wrote: >> [...] >> > > What about !PREEMPT_RT? We have people running isolated workloads and >> > > these sorts of pcp disruptions are really unwelcome as well. They do not >> > > have requirements as strong as RT workloads but the underlying >> > > fundamental problem is the same. Frederic (now CCed) is working on >> > > moving those pcp book keeping activities to be executed to the return to >> > > the userspace which should be taking care of both RT and non-RT >> > > configurations AFAICS. >> > >> > Michal, >> > >> > For !PREEMPT_RT, _if_ you select CONFIG_QPW=y, then there is a kernel >> > boot option qpw=y/n, which controls whether the behaviour will be >> > similar (the spinlock is taken on local_lock, similar to PREEMPT_RT). >> >> My bad. I've misread the config space of this. > > My bad, actually. Its only CONFIG_QPW on the current patchset. > >> > If CONFIG_QPW=n, or kernel boot option qpw=n, then only local_lock >> > (and remote work via work_queue) is used. >> > >> > What "pcp book keeping activities" you refer to ? I don't see how >> > moving certain activities that happen under SLUB or LRU spinlocks >> > to happen before return to userspace changes things related >> > to avoidance of CPU interruption ? >> >> Essentially delayed operations like pcp state flushing happens on return >> to the userspace on isolated CPUs. No locking changes are required as >> the work is still per-cpu. >> >> In other words the approach Frederic is working on is to not change the >> locking of pcp delayed work but instead move that work into well defined >> place - i.e. return to the userspace. >> >> Btw. have you measure the impact of preempt_disbale -> spinlock on hot >> paths like SLUB sheeves? > > Nope, i have not. What is/are the standard benchmarks for SLUB/SLAB > allocation ? Those mentioned here, and I would say also netperf. https://lore.kernel.org/all/20250913000935.1021068-1-sudarsanm@google.com/