From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id E6C83C54E71 for ; Tue, 20 May 2025 20:34:31 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7DDCD6B0093; Tue, 20 May 2025 16:34:31 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7675F6B0095; Tue, 20 May 2025 16:34:31 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 67ED06B0096; Tue, 20 May 2025 16:34:31 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 45A766B0093 for ; Tue, 20 May 2025 16:34:31 -0400 (EDT) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 86C03BEC52 for ; Tue, 20 May 2025 20:34:30 +0000 (UTC) X-FDA: 83464439100.02.8514DF4 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) by imf02.hostedemail.com (Postfix) with ESMTP id AFD618000D for ; Tue, 20 May 2025 20:34:27 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=none; spf=pass (imf02.hostedemail.com: domain of riel@shelob.surriel.com designates 96.67.55.147 as permitted sender) smtp.mailfrom=riel@shelob.surriel.com; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1747773267; h=from:from:sender:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ZAKqfEk5wNkSxchE2mlMppcXllbhtMFBGsoAzbBLQxA=; b=qAUS7+zZKkT9/Ce+Hn7wVbT8f++BpYCssmJn0hXf179fXEcaX6aqNHtEy4TD0dpA7PaCxF OcxnI0W02fKmArDAH17Rd1XoZT7QriUH8ZUkQ893fOJrfzbmnfHzOZK738RgRG2rOnNKZU cJn0hAWGoyhYlM4F9UYVGR460oDc2GI= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1747773267; a=rsa-sha256; cv=none; b=B5QmOLIBmaaA+4mifaax+6YrbaDD7annIWukBIKieUTDDtRKKRGi3e4VvzLeVDlhPcs1a+ 8cKMOkdmNrr8yHNyK0ZvoMNZg+8hJQHRkNSM+HCCYg4aj1gUmFgEJjpqDofefSJbTV4mOR C0xNEEf6dBqZpfUri2bFavBkFGlo2nY= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=none; spf=pass (imf02.hostedemail.com: domain of riel@shelob.surriel.com designates 96.67.55.147 as permitted sender) smtp.mailfrom=riel@shelob.surriel.com; dmarc=none Received: from fangorn.home.surriel.com ([10.0.13.7]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.97.1) (envelope-from ) id 1uHTcK-000000007yU-3VQB; Tue, 20 May 2025 16:31:16 -0400 Message-ID: <1debe11314379cd767c5f75131e81eed70670b91.camel@surriel.com> Subject: Re: [RFC v2 7/9] x86/mm: Introduce Remote Action Request From: Rik van Riel To: Nadav Amit Cc: Linux Kernel Mailing List , "open list:MEMORY MANAGEMENT" , the arch/x86 maintainers , kernel-team@meta.com, Dave Hansen , luto@kernel.org, peterz@infradead.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Yu-cheng Yu Date: Tue, 20 May 2025 16:31:16 -0400 In-Reply-To: <4009A0C6-CE5C-4197-9F48-3805059C214E@gmail.com> References: <20250520010350.1740223-1-riel@surriel.com> <20250520010350.1740223-8-riel@surriel.com> <4A879001-E213-4239-9D25-CDA8EC3E2CD9@gmail.com> <6a3290319031cd68a383e416f53aa7549bac9407.camel@surriel.com> <4009A0C6-CE5C-4197-9F48-3805059C214E@gmail.com> Autocrypt: addr=riel@surriel.com; prefer-encrypt=mutual; keydata=mQENBFIt3aUBCADCK0LicyCYyMa0E1lodCDUBf6G+6C5UXKG1jEYwQu49cc/gUBTTk33A eo2hjn4JinVaPF3zfZprnKMEGGv4dHvEOCPWiNhlz5RtqH3SKJllq2dpeMS9RqbMvDA36rlJIIo47 Z/nl6IA8MDhSqyqdnTY8z7LnQHqq16jAqwo7Ll9qALXz4yG1ZdSCmo80VPetBZZPw7WMjo+1hByv/ lvdFnLfiQ52tayuuC1r9x2qZ/SYWd2M4p/f5CLmvG9UcnkbYFsKWz8bwOBWKg1PQcaYHLx06sHGdY dIDaeVvkIfMFwAprSo5EFU+aes2VB2ZjugOTbkkW2aPSWTRsBhPHhV6dABEBAAG0HlJpayB2YW4gU mllbCA8cmllbEByZWRoYXQuY29tPokBHwQwAQIACQUCW5LcVgIdIAAKCRDOed6ShMTeg05SB/986o gEgdq4byrtaBQKFg5LWfd8e+h+QzLOg/T8mSS3dJzFXe5JBOfvYg7Bj47xXi9I5sM+I9Lu9+1XVb/ r2rGJrU1DwA09TnmyFtK76bgMF0sBEh1ECILYNQTEIemzNFwOWLZZlEhZFRJsZyX+mtEp/WQIygHV WjwuP69VJw+fPQvLOGn4j8W9QXuvhha7u1QJ7mYx4dLGHrZlHdwDsqpvWsW+3rsIqs1BBe5/Itz9o 6y9gLNtQzwmSDioV8KhF85VmYInslhv5tUtMEppfdTLyX4SUKh8ftNIVmH9mXyRCZclSoa6IMd635 Jq1Pj2/Lp64tOzSvN5Y9zaiCc5FucXtB9SaWsgdmFuIFJpZWwgPHJpZWxAc3VycmllbC5jb20+iQE +BBMBAgAoBQJSLd2lAhsjBQkSzAMABgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRDOed6ShMTe g4PpB/0ZivKYFt0LaB22ssWUrBoeNWCP1NY/lkq2QbPhR3agLB7ZXI97PF2z/5QD9Fuy/FD/jddPx KRTvFCtHcEzTOcFjBmf52uqgt3U40H9GM++0IM0yHusd9EzlaWsbp09vsAV2DwdqS69x9RPbvE/Ne fO5subhocH76okcF/aQiQ+oj2j6LJZGBJBVigOHg+4zyzdDgKM+jp0bvDI51KQ4XfxV593OhvkS3z 3FPx0CE7l62WhWrieHyBblqvkTYgJ6dq4bsYpqxxGJOkQ47WpEUx6onH+rImWmPJbSYGhwBzTo0Mm G1Nb1qGPG+mTrSmJjDRxrwf1zjmYqQreWVSFEt26tBpSaWsgdmFuIFJpZWwgPHJpZWxAZmIuY29tP okBPgQTAQIAKAUCW5LbiAIbIwUJEswDAAYLCQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQznneko TE3oOUEQgAsrGxjTC1bGtZyuvyQPcXclap11Ogib6rQywGYu6/Mnkbd6hbyY3wpdyQii/cas2S44N cQj8HkGv91JLVE24/Wt0gITPCH3rLVJJDGQxprHTVDs1t1RAbsbp0XTksZPCNWDGYIBo2aHDwErhI omYQ0Xluo1WBtH/UmHgirHvclsou1Ks9jyTxiPyUKRfae7GNOFiX99+ZlB27P3t8CjtSO831Ij0Ip QrfooZ21YVlUKw0Wy6Ll8EyefyrEYSh8KTm8dQj4O7xxvdg865TLeLpho5PwDRF+/mR3qi8CdGbkE c4pYZQO8UDXUN4S+pe0aTeTqlYw8rRHWF9TnvtpcNzZw== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.3 (3.54.3-1.fc41) MIME-Version: 1.0 X-Stat-Signature: tsfhbejrj8m76tea8899jd4meemfzbcj X-Rspamd-Queue-Id: AFD618000D X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1747773267-311742 X-HE-Meta: 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 5p+5ul54 xqFtt0qfz25yvCqNNyhl27tlPmNQQwpUlmYUH4dIbzCJvRUeE17X8PiywC/rCv09WowtkxVSEoJRuIid9dyiUx1gRfP2wJaMJDf85bpp+Mh1Xy0TeNTG43FOkVgpcZp4ceY0mF1iHAjIoH2SYWyPj7J1JIGJr8qUjgwt/MFRfRvyNViTsvFoJZ8xYf0f3ZQkN0pNUkppA/ZbPnIp61VjfKwWc/DwWnCwT1FepbJ+Q70R1eVBY+cjzj/tHWp+vNOsBv1aDTtxAxlSYKg+2uXOHIY+f1BXbHuY/7aVCif9N7gV5B14dxh0FuGD/lC1QmLip8oAAUy0BEw/CFeOKLCYdDOFI+dEyQgk9i4tpdJwn9inT7SQlDy5kLmmwJWcK1fJObTf1MgcBlJSgV8M= 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 Tue, 2025-05-20 at 23:26 +0300, Nadav Amit wrote: >=20 > > On 20 May 2025, at 16:00, Rik van Riel wrote: > >=20 > > > Putting aside the rest of the code, I see you don=E2=80=99t call > > > should_flush_tlb(). > > > I think it is worth mentioning in commit log or comment the > > > rationale > > > behind > > > it (and maybe benchmarks to justify it). > > >=20 > > >=20 > > The long term plan here is to simply have the originating > > CPU included in the cpumask, and have it send a RAR > > request to itself. >=20 > That=E2=80=99s unrelated. I was referring to considering supporting > some sort of lazy TLB to eliminate sending RAR to cores that > do not care about it. Is there a cost of RAR to more cores than > needed? My guess is that there is one, and maybe in such cases > you would want actual IPI and special handling. For RAR, I suspect the big cost is waking up CPUs in idle states, and waiting for them to wake up. One possibility may be to change leave_mm() to have an argument to set some flag that the RAR code can read to see whether or not to send a RAR interrupt to that CPU, even if it is in the cpumask. I don't think we can use the exact same should_flush_tlb() logic, because the tlb_gen is not updated by a RAR flush, and the should_flush_tlb() logic is somewhat intertwined with the tlb_gen logic. --=20 All Rights Reversed.