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 BDA44C433EF for ; Sun, 9 Jan 2022 19:22:25 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 204206B0071; Sun, 9 Jan 2022 14:22:25 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 1B33F6B0073; Sun, 9 Jan 2022 14:22:25 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0A3216B0074; Sun, 9 Jan 2022 14:22:25 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0080.hostedemail.com [216.40.44.80]) by kanga.kvack.org (Postfix) with ESMTP id EF4036B0071 for ; Sun, 9 Jan 2022 14:22:24 -0500 (EST) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id A57ED824C421 for ; Sun, 9 Jan 2022 19:22:24 +0000 (UTC) X-FDA: 79011719808.21.E26E37E Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) by imf25.hostedemail.com (Postfix) with ESMTP id DE574A0008 for ; Sun, 9 Jan 2022 19:22:21 +0000 (UTC) Received: from imladris.surriel.com ([96.67.55.152]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1n6dlb-0007k0-8a; Sun, 09 Jan 2022 14:22:11 -0500 Message-ID: Subject: Re: [PATCH 16/23] sched: Use lightweight hazard pointers to grab lazy mms From: Rik van Riel To: Nadav Amit , Linus Torvalds , Andy Lutomirski Cc: Andrew Morton , Linux-MM , Nicholas Piggin , Anton Blanchard , Benjamin Herrenschmidt , Paul Mackerras , Randy Dunlap , linux-arch , X86 ML , Dave Hansen , Peter Zijlstra , Mathieu Desnoyers Date: Sun, 09 Jan 2022 14:22:10 -0500 In-Reply-To: References: <7c9c388c388df8e88bb5d14828053ac0cb11cf69.1641659630.git.luto@kernel.org> <739A3109-04DD-4BA5-A02B-52EE30E820AE@gmail.com> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-3bYF5AhkVoIli31LXQXk" User-Agent: Evolution 3.40.3 (3.40.3-1.fc34) MIME-Version: 1.0 X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: DE574A0008 X-Stat-Signature: n5yj4454kxkuj11ucof1h8wxj3pznxxf Authentication-Results: imf25.hostedemail.com; dkim=none; spf=none (imf25.hostedemail.com: domain of riel@shelob.surriel.com has no SPF policy when checking 96.67.55.147) smtp.mailfrom=riel@shelob.surriel.com; dmarc=none X-HE-Tag: 1641756141-932013 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: --=-3bYF5AhkVoIli31LXQXk Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, 2022-01-09 at 00:49 -0800, Nadav Amit wrote: >=20 > It is possible for instance to get rid of is_lazy, keep the CPU > on mm_cpumask when switching to kernel thread, and then if/when > an IPI is received remove it from cpumask to avoid further > unnecessary TLB shootdown IPIs. >=20 > I do not know whether it is a pure win, but there is a tradeoff. That's not a win at all. It is what we used to have before the lazy mm stuff was re-introduced, and it led to quite a few unnecessary IPIs, which are especially slow on virtual machines, where the target CPU may not be running. --=20 All Rights Reversed. --=-3bYF5AhkVoIli31LXQXk Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEEKR73pCCtJ5Xj3yADznnekoTE3oMFAmHbNeIACgkQznnekoTE 3oO3dAgAnFIAWZSgHJZ3+KDjfwPiBN0+9hgcTu2bwk1/RcslCWYksrooQ8MPI8Sl NQmy31fqVLA5x0bmynjpS30u4hDl7qywvazXv8Z+CGh3IDoilsbF83Gf/ZkH6NCa bQKj5/ujChp33NHLyVCHq5hHNP6iLm0V2DVb/tSInTsVcR4C3CiCzO2dDKt306DG spuz5xx8i4WeU4mQs6+3aSD6UQobhVozIKaYyaD5RAFLf4yVMgrhfxcojOtU0F4B Ot2LmnTn2cKPZJldGPsnLkGmH4NiaXfvsetBaOXH91TR7DWsbLtNOso59qzvra6+ WFjZVTZ3AMx8EK3a1AOeIBUZiJ/GRg== =lb9o -----END PGP SIGNATURE----- --=-3bYF5AhkVoIli31LXQXk--