From owner-freebsd-virtualization@freebsd.org Tue Nov 27 23:06:43 2018 Return-Path: Delivered-To: freebsd-virtualization@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 0D045113EFC5 for ; Tue, 27 Nov 2018 23:06:43 +0000 (UTC) (envelope-from freebsd-rwg@pdx.rh.CN85.dnsmgr.net) Received: from pdx.rh.CN85.dnsmgr.net (br1.CN84in.dnsmgr.net [69.59.192.140]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 5023D74055 for ; Tue, 27 Nov 2018 23:06:42 +0000 (UTC) (envelope-from freebsd-rwg@pdx.rh.CN85.dnsmgr.net) Received: from pdx.rh.CN85.dnsmgr.net (localhost [127.0.0.1]) by pdx.rh.CN85.dnsmgr.net (8.13.3/8.13.3) with ESMTP id wARN6dPe003728; Tue, 27 Nov 2018 15:06:39 -0800 (PST) (envelope-from freebsd-rwg@pdx.rh.CN85.dnsmgr.net) Received: (from freebsd-rwg@localhost) by pdx.rh.CN85.dnsmgr.net (8.13.3/8.13.3/Submit) id wARN6dKU003727; Tue, 27 Nov 2018 15:06:39 -0800 (PST) (envelope-from freebsd-rwg) From: "Rodney W. Grimes" Message-Id: <201811272306.wARN6dKU003727@pdx.rh.CN85.dnsmgr.net> Subject: Re: Any plans to increase the maximum number of virtual CPUs above 16? In-Reply-To: <331a93ae-d4d8-e510-4499-7185e31fbbc9@gmail.com> To: Simon Connah Date: Tue, 27 Nov 2018 15:06:39 -0800 (PST) CC: "freebsd-virtualization@freebsd.org" X-Mailer: ELM [version 2.4ME+ PL121h (25)] MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 5023D74055 X-Spamd-Result: default: False [2.42 / 15.00]; ARC_NA(0.00)[]; TO_DN_EQ_ADDR_SOME(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; MIME_GOOD(-0.10)[text/plain]; RCVD_TLS_LAST(0.00)[]; DMARC_NA(0.00)[dnsmgr.net]; AUTH_NA(1.00)[]; NEURAL_SPAM_MEDIUM(0.57)[0.571,0]; RCVD_COUNT_THREE(0.00)[3]; TO_MATCH_ENVRCPT_SOME(0.00)[]; MX_GOOD(-0.01)[cached: pdx.rh.CN85.dnsmgr.net]; RCPT_COUNT_TWO(0.00)[2]; NEURAL_SPAM_LONG(0.04)[0.038,0]; NEURAL_HAM_SHORT(-0.06)[-0.063,0]; R_SPF_NA(0.00)[]; FREEMAIL_TO(0.00)[gmail.com]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; SUBJECT_ENDS_QUESTION(1.00)[]; ASN(0.00)[asn:13868, ipnet:69.59.192.0/19, country:US]; MID_RHS_MATCH_FROM(0.00)[]; IP_SCORE(-0.02)[country: US(-0.09)] X-Rspamd-Server: mx1.freebsd.org X-BeenThere: freebsd-virtualization@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "Discussion of various virtualization techniques FreeBSD supports." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 27 Nov 2018 23:06:43 -0000 > I was reading the bhyve man page and noticed that it said the maximum > number of virtual CPUs is limited to 16. With AMD Epyc being out with 32 > cores and 64 threads per CPU and being able to have 2 of them in one > system this number seems rather low by modern standards. So you can run 4 x 16 vcpu VM's, probably more common than someone trying to run 1 VM of 32 or 64 vcpu. > > Are there any plans to increase this number to something like 32 virtual > CPUs? There is work in process to change this from a compile time kernel constant to a per VM value set using the undocumnted, but present value in the cpu_topology option max_cpu. We do not want to just crank this value up as data structures for each VM are sized on the MAXCPU connstant, and doubling that to 32 would be fairly wasteful for low core count VM's. -- Rod Grimes rgrimes@freebsd.org