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t=1785862054; bh=/m4yAZ5mIsOFZEiU4veHFKr2AoqsHnJrC8u0FSLN/U8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=KAAuqSzDp0wplUBF9Fq0YxQTEF733hGX4xj4Y90DI8bZ9hL6VeW908wQGHnfPdsZu rrCzEKEjeah6szU+pl4/gkNRp/qVwmNa+ywme1I4lHz2SuIjJP5BWpFfGVgNYA9Eo4 v9vjxuwD+2Hyaigth9wcOM+k8DBaj/CIgX7XW4LMIS9cw03FKnhczraAQ7g2I/cQrE bbnOGQeUiAJAqPJElj7deWCtVPBmTP81tXGPOIZaY1hjfVOreivQ/k5PuK/I13vFzF CRX3ouvSBJ635W/6cspzFiRlHWV0BzyJiBOZs8jir0u29LyxpLKQHNzprXKiaDAND6 Np0mwa4lS6oug== Message-ID: <84b31836-1d10-4bec-a469-468b91fd4645@kernel.org> Date: Tue, 4 Aug 2026 18:47:26 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v2 PATCH 0/16] Optimize this_cpu_*() ops for non-x86 (ARM64 for this series) To: "Christoph Lameter (Ampere)" , "Lorenzo Stoakes (ARM)" Cc: Mark Rutland , Yang Shi , Ryan Roberts , dennis@kernel.org, tj@kernel.org, urezki@gmail.com, catalin.marinas@arm.com, will@kernel.org, akpm@linux-foundation.org, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Linus Torvalds , Jason Gunthorpe References: <20260715180455.515692-1-yang@os.amperecomputing.com> <0344c559-1959-4531-9265-d5a5180eb7cd@arm.com> <25d1e09b-53e4-7cd5-87db-b58437e4e690@gentwo.org> <4887267b-dc26-4c33-96ca-8dff054a0d1f@kernel.org> <63ea8156-a109-b2a2-6d35-1c17ad7f1a9d@gentwo.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 3030A80010 X-Stat-Signature: i5ar8seg7xrautuupmxhj8xew3u5edpb X-Rspam-User: X-HE-Tag: 1785862056-416990 X-HE-Meta: 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 2wnzjDws bAL0VYYQx1Osf4QDrHfpZ0tFgSkxCjplXOZKlQXwnlDhzIWhMshgO5hL7TlH/Tgnk2pnpM5aFtEc2gIAiS3MBO8ruxQEbp3vg+rrBqHz9XjJffr6U93bOWhbYD6lawyzPVyBSo18HTAHdtm2HgSIm1cJ45AXv6OIPUhXW8B10atEvngDVDq+K+JpM39WJ7XPlvhRZpJE5ZTCPOgqmzK9qPbtw0X4qFR1U8bPAj2ZQ1N28h6OvzCNHJGMPALLGbkdBqIgZjMPAv6LpMiRJ6aGeg2sJGHtYgfka/0GfHuCukbIYxZf3M4DXM99nM+82S1d4dNubJCadT2oB+4txOyNUaxjFMnSxJfVYietC Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/4/26 18:19, Christoph Lameter (Ampere) wrote: > On Tue, 4 Aug 2026, Lorenzo Stoakes (ARM) wrote: > >> Since this work seems to be very much arm64-focused, perhaps it's therefore >> worth looking at an alterative solution that's specific to the arch, like the >> one suggested by Mark ([1])? >> >> [0]:https://lore.kernel.org/all/CAHk-=wire3dzhHx=KiL_f5Rj0=1u9ustsa33QoR-F9-v-NU9Ng@mail.gmail.com/ >> [1]:https://lore.kernel.org/linux-arm-kernel/al_DpFJFcmVhxpvW@J2N7QTR9R3/ > > Mark's solution does replace the preempt_enable/disable sections with a > rather hacky restart logic. It relies on a long preemable and postscript > to each per cpu operations. Okay, so 3 simple instructions of preemable is "long preemable"? In which universe? But I am sure you did you homework and have data to back up your claims. Please share that data, because I am very curious. > > It does not remove the code entirely like the proposed patchset here and > cannot produce the same compact code as x86. Mark's solution is the obvious improvement to the problem, doing it just like s390 already does. If the proposed solution has a significant benefit over Mark's solution it could be discussed as a next step; and it must be backed with sufficient data to warrant all this complexity here. -- Cheers, David