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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 F2CE1C43381 for ; Fri, 22 Feb 2019 10:24:27 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 A26B120645 for ; Fri, 22 Feb 2019 10:24:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A26B120645 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 445SBK57J7zDq7k for ; Fri, 22 Feb 2019 21:24:25 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 445RND2rKWzDqB3 for ; Fri, 22 Feb 2019 20:47:56 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Received: by ozlabs.org (Postfix) id 445RNC6KmQz9sNQ; Fri, 22 Feb 2019 20:47:55 +1100 (AEDT) Received: by ozlabs.org (Postfix, from userid 1034) id 445RNC1yrvz9sMx; Fri, 22 Feb 2019 20:47:53 +1100 (AEDT) X-powerpc-patch-notification: thanks X-powerpc-patch-commit: 19f8a5b5be2898573a5e1dc1db93e8d40117606a X-Patchwork-Hint: ignore In-Reply-To: <20190212005829.GB7353@blackberry> To: Paul Mackerras , linuxppc-dev@ozlabs.org From: Michael Ellerman Subject: Re: powerpc/powernv: Don't reprogram SLW image on every KVM guest entry/exit Message-Id: <445RNC1yrvz9sMx@ozlabs.org> Date: Fri, 22 Feb 2019 20:47:53 +1100 (AEDT) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Michael Ellerman , "Gautham R. Shenoy" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, 2019-02-12 at 00:58:29 UTC, Paul Mackerras wrote: > Commit 24be85a23d1f ("powerpc/powernv: Clear PECE1 in LPCR via stop-api > only on Hotplug", 2017-07-21) added two calls to opal_slw_set_reg() > inside pnv_cpu_offline(), with the aim of changing the LPCR value in > the SLW image to disable wakeups from the decrementer while a CPU is > offline. However, pnv_cpu_offline() gets called each time a secondary > CPU thread is woken up to participate in running a KVM guest, that is, > not just when a CPU is offlined. > > Since opal_slw_set_reg() is a very slow operation (with observed > execution times around 20 milliseconds), this means that an offline > secondary CPU can often be busy doing the opal_slw_set_reg() call > when the primary CPU wants to grab all the secondary threads so that > it can run a KVM guest. This leads to messages like "KVM: couldn't > grab CPU n" being printed and guest execution failing. > > There is no need to reprogram the SLW image on every KVM guest entry > and exit. So that we do it only when a CPU is really transitioning > between online and offline, this moves the calls to > pnv_program_cpu_hotplug_lpcr() into pnv_smp_cpu_kill_self(). > > Fixes: 24be85a23d1f ("powerpc/powernv: Clear PECE1 in LPCR via stop-api only on Hotplug") > Cc: stable@vger.kernel.org # v4.14+ > Signed-off-by: Paul Mackerras Applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/19f8a5b5be2898573a5e1dc1db93e8d4 cheers