From owner-freebsd-hackers@freebsd.org Thu Sep 17 18:38:35 2020 Return-Path: Delivered-To: freebsd-hackers@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 6D3FF3E9EB2 for ; Thu, 17 Sep 2020 18:38:35 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4Bsm222bsNz4R2D; Thu, 17 Sep 2020 18:38:33 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.16.1/8.16.1) with ESMTPS id 08HIcPot060419 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Thu, 17 Sep 2020 21:38:29 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua 08HIcPot060419 Received: (from kostik@localhost) by tom.home (8.16.1/8.16.1/Submit) id 08HIcP8G060418; Thu, 17 Sep 2020 21:38:25 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Thu, 17 Sep 2020 21:38:25 +0300 From: Konstantin Belousov To: Wei Hu , avg@freebsd.org Cc: "freebsd-hackers@freebsd.org" Subject: Re: MSR accesses that slows down the hypervisor/host Message-ID: <20200917183825.GU94807@kib.kiev.ua> References: <20200916135727.GO94807@kib.kiev.ua> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FROM, NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on tom.home X-Rspamd-Queue-Id: 4Bsm222bsNz4R2D X-Spamd-Bar: / Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=fail reason="No valid SPF, No valid DKIM" header.from=gmail.com (policy=none); spf=softfail (mx1.freebsd.org: 2001:470:d5e7:1::1 is neither permitted nor denied by domain of kostikbel@gmail.com) smtp.mailfrom=kostikbel@gmail.com X-Spamd-Result: default: False [0.51 / 15.00]; ARC_NA(0.00)[]; TO_DN_EQ_ADDR_SOME(0.00)[]; DMARC_POLICY_SOFTFAIL(0.10)[gmail.com : No valid SPF, No valid DKIM,none]; RCVD_TLS_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[3]; FREEMAIL_FROM(0.00)[gmail.com]; NEURAL_SPAM_SHORT(0.30)[0.301]; MIME_GOOD(-0.10)[text/plain]; HAS_XAW(0.00)[]; NEURAL_HAM_MEDIUM(-0.19)[-0.191]; R_SPF_SOFTFAIL(0.00)[~all:c]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_SOME(0.00)[]; NEURAL_SPAM_LONG(0.40)[0.398]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:6939, ipnet:2001:470::/32, country:US]; MIME_TRACE(0.00)[0:+]; MAILMAN_DEST(0.00)[freebsd-hackers]; RCVD_COUNT_TWO(0.00)[2] X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.33 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 17 Sep 2020 18:38:35 -0000 On Thu, Sep 17, 2020 at 05:34:22AM +0000, Wei Hu wrote: > > From: Konstantin Belousov > > Sent: Wednesday, September 16, 2020 9:57 PM > > To: Wei Hu > > Cc: freebsd-hackers@freebsd.org > > Subject: Re: MSR accesses that slows down the hypervisor/host > > > > Where do you see accesses to MSR_LS_CFG ? I can only find manipulations of > > that MSR in init_amd(), and then it is all under check that we are not > > virtualized. > > > Yes, it is only accessed in init_amd() at boot time. So it is less concerned. MSR_AMDK8_IPM > is accessed in cpu_idle() all the time, so it is the key place to optimize. > > > For MSR_AMDK8_IPM access in cpu_idle(), it seems that the workaround was > > applied too wide. It might be that we do not need to do it on recent CPUs, but I > > need to spent more time looking at datasheets to confirm/deny. > > > > But, do you (hypervisor) indeed allow guest to initiate C1 or deeper idle state ? > > If not, perhaps as the first measure, we can avoid manipulating > > MSR_AMDK8_IPM under hypervisor at all. > > You are right a guest cannot initiate C1 or deeper idle state when running on Hyper-V. > So skipping the read of MSR_AMDK8_IPM when running under this hypervisor would > Be a viable solution. https://reviews.freebsd.org/D26470