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 X-Spam-Level: X-Spam-Status: No, score=-10.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8E05CC433E2 for ; Tue, 1 Sep 2020 09:27:17 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 55514205CB for ; Tue, 1 Sep 2020 09:27:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="ywEUjpl7" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 55514205CB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=BWI62Bbavnu4FCEMeSYoIEWUL3E1xlyQtz0pMSsC50E=; b=ywEUjpl7aUf8z+s5a4dhXucrM EsTHMiutWu2sMaMQm+dyYDBK5KPkeVcWlqCet5I/26lklNHNESCjCGmGP6TwH1qai8LoVHLATkqS4 2FaIXdZff/ynDamOdssC3Brn2/Mq040XY5/3O7vfMr8xGKE3RNoq433AUanYxBL2a8egCUHrmEn/1 ooCYAvk4BzSXXImLytwBUkD+QB+gWlPMK1miX9h45SneBLGBpCfaMqmGRiG9vyT+bD7wM0r4PGxyM YBmdsrD8sCUY40fFIia/9aLdoGGRlutxWoVSyY+pwl4LUW/llS2q2a0azQ0iPZQzUQzibePP7VTdc KDJoGtfjw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kD2YC-000349-0s; Tue, 01 Sep 2020 09:26:00 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kD2Y8-00033K-SH for linux-arm-kernel@lists.infradead.org; Tue, 01 Sep 2020 09:25:58 +0000 Received: from gaia (unknown [46.69.195.127]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8FE6D206A5; Tue, 1 Sep 2020 09:25:54 +0000 (UTC) Date: Tue, 1 Sep 2020 10:25:52 +0100 From: Catalin Marinas To: Shuah Khan Subject: Re: [PATCH v3 0/5] arm64: vdso: getcpu() support Message-ID: <20200901092551.GG5561@gaia> References: <20200819121318.52158-1-broonie@kernel.org> <315d97af-715a-9942-a731-11de2fbbbded@linuxfoundation.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <315d97af-715a-9942-a731-11de2fbbbded@linuxfoundation.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200901_052557_067657_2339721A X-CRM114-Status: GOOD ( 35.85 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Will Deacon , Mark Brown , linux-kselftest@vger.kernel.org, Vincenzo Frascino , Shuah Khan , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Aug 31, 2020 at 03:47:17PM -0600, Shuah Khan wrote: > On 8/19/20 6:13 AM, Mark Brown wrote: > > Some applications, especially tracing ones, benefit from avoiding the > > syscall overhead for getcpu() so it is common for architectures to have > > vDSO implementations. Add one for arm64, using TPIDRRO_EL0 to pass a > > pointer to per-CPU data rather than just store the immediate value in > > order to allow for future extensibility. > > > > It is questionable if something TPIDRRO_EL0 based is worthwhile at all > > on current kernels, since v4.18 we have had support for restartable > > sequences which can be used to provide a sched_getcpu() implementation > > with generally better performance than the vDSO approach on > > architectures which have that[1]. Work is ongoing to implement this for > > glibc: > > > > https://lore.kernel.org/lkml/20200527185130.5604-3-mathieu.desnoyers@efficios.com/ > > > > but is not yet merged and will need similar work for other userspaces. > > The main advantages for the vDSO implementation are the node parameter > > (though this is a static mapping to CPU number so could be looked up > > separately when processing data if it's needed, it shouldn't need to be > > in the hot path) and ease of implementation for users. > > > > This is currently not compatible with KPTI due to the use of TPIDRRO_EL0 > > by the KPTI trampoline, this could be addressed by reinitializing that > > system register in the return path but I have found it hard to justify > > adding that overhead for all users for something that is essentially a > > profiling optimization which is likely to get superceeded by a more > > modern implementation - if there are other uses for the per-CPU data > > then the balance might change here. > > > > This builds on work done by Kristina Martsenko some time ago but is a > > new implementation. > > > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d7822b1e24f2df5df98c76f0e94a5416349ff759 > > > > v3: > > - Rebase on v5.9-rc1. > > - Drop in progress portions of the series. > > v2: > > - Rebase on v5.8-rc3. > > - Add further cleanup patches & a first draft of multi-page support. > > > > Mark Brown (5): > > arm64: vdso: Provide a define when building the vDSO > > arm64: vdso: Add per-CPU data > > arm64: vdso: Initialise the per-CPU vDSO data > > arm64: vdso: Add getcpu() implementation > > selftests: vdso: Support arm64 in getcpu() test > > > > arch/arm64/include/asm/processor.h | 12 +---- > > arch/arm64/include/asm/vdso/datapage.h | 54 +++++++++++++++++++ > > arch/arm64/kernel/process.c | 26 ++++++++- > > arch/arm64/kernel/vdso.c | 33 +++++++++++- > > arch/arm64/kernel/vdso/Makefile | 4 +- > > arch/arm64/kernel/vdso/vdso.lds.S | 1 + > > arch/arm64/kernel/vdso/vgetcpu.c | 48 +++++++++++++++++ > > .../testing/selftests/vDSO/vdso_test_getcpu.c | 10 ++++ > > 8 files changed, 172 insertions(+), 16 deletions(-) > > create mode 100644 arch/arm64/include/asm/vdso/datapage.h > > create mode 100644 arch/arm64/kernel/vdso/vgetcpu.c > > > > Patches look good to me from selftests perspective. My acked by > for these patches to go through arm64. > > Acked-by: Shuah Khan > > If you would like me to take these through kselftest tree, give > me your Acks. I can queue these up for 5.10-rc1 Thanks Shuah for the ack. We are still pondering whether the merge these patches as they have some limitations (the per-CPU data structures may not fit in the sole data vDSO page). -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel