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[69.159.36.102]) by smtp.gmail.com with ESMTPSA id a16sm2098155itc.27.2019.03.20.20.49.21 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 20 Mar 2019 20:49:21 -0700 (PDT) Sender: Mark Johnston Date: Wed, 20 Mar 2019 23:49:17 -0400 From: Mark Johnston To: rgrimes@freebsd.org Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r345359 - in head/sys/cddl/dev/dtrace: amd64 i386 Message-ID: <20190321034917.GA8186@raichu> References: <201903210252.x2L2qMSP022374@repo.freebsd.org> <201903210320.x2L3KIjc058579@gndrsh.dnsmgr.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201903210320.x2L3KIjc058579@gndrsh.dnsmgr.net> User-Agent: Mutt/1.11.3 (2019-02-01) X-Rspamd-Queue-Id: 64D876B255 X-Spamd-Bar: ----- Authentication-Results: mx1.freebsd.org; dkim=pass header.d=gmail.com header.s=20161025 header.b=revQkOoN; spf=pass (mx1.freebsd.org: domain of markjdb@gmail.com designates 2607:f8b0:4864:20::129 as permitted sender) smtp.mailfrom=markjdb@gmail.com X-Spamd-Result: default: False [-5.43 / 15.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_DKIM_ALLOW(-0.20)[gmail.com:s=20161025]; NEURAL_HAM_MEDIUM(-1.00)[-1.000,0]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[4]; R_SPF_ALLOW(-0.20)[+ip6:2607:f8b0:4000::/36]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_GOOD(-0.10)[text/plain]; TO_DN_NONE(0.00)[]; DMARC_NA(0.00)[freebsd.org]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; RCVD_COUNT_THREE(0.00)[3]; RCVD_TLS_LAST(0.00)[]; DKIM_TRACE(0.00)[gmail.com:+]; MX_GOOD(-0.01)[cached: alt3.gmail-smtp-in.l.google.com]; RCVD_IN_DNSWL_NONE(0.00)[9.2.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.0.0.4.6.8.4.0.b.8.f.7.0.6.2.list.dnswl.org : 127.0.5.0]; NEURAL_HAM_SHORT(-0.95)[-0.952,0]; IP_SCORE(-2.77)[ip: (-8.83), ipnet: 2607:f8b0::/32(-2.81), asn: 15169(-2.12), country: US(-0.07)]; FORGED_SENDER(0.30)[markj@freebsd.org,markjdb@gmail.com]; MIME_TRACE(0.00)[0:+]; MID_RHS_NOT_FQDN(0.50)[]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:15169, ipnet:2607:f8b0::/32, country:US]; FROM_NEQ_ENVFROM(0.00)[markj@freebsd.org,markjdb@gmail.com] X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 21 Mar 2019 03:49:25 -0000 On Wed, Mar 20, 2019 at 08:20:18PM -0700, Rodney W. Grimes wrote: > > Author: markj > > Date: Thu Mar 21 02:52:22 2019 > > New Revision: 345359 > > URL: https://svnweb.freebsd.org/changeset/base/345359 > > > > Log: > > Don't attempt to measure TSC skew when running as a VM guest. > > > > It simply doesn't work in general since VCPUs may migrate between > > physical cores. The approach used to measure skew also doesn't > > make much sense in a VM. > > "May" is the important aspect here, and to my knowledge both > bhyve and Vmware provide a way to pin cpus there should be > a way for us to turn this back on if it is desired. Sticking > it under the big knob vm_guest is probably not the most flexiable > solution. > > Could we please have someway to force this back on? Even with pinning the skew computation is bogus in a VM. On an idle host running bhyve with pinned vCPUs it gives offsets that are several orders of magnitude larger than on the host. I would prefer to see a specific reason for wanting the old behaviour before adding a knob.