From owner-svn-src-head@freebsd.org Mon Dec 11 15:22:28 2017 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 17E91E94D23; Mon, 11 Dec 2017 15:22:28 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 993ED6A0F8; Mon, 11 Dec 2017 15:22:27 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id vBBFMJP7081859 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Mon, 11 Dec 2017 17:22:23 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua vBBFMJP7081859 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id vBBFMJJW081858; Mon, 11 Dec 2017 17:22:19 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Mon, 11 Dec 2017 17:22:19 +0200 From: Konstantin Belousov To: rgrimes@freebsd.org Cc: Conrad Meyer , src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r326758 - in head/sys/i386: conf include Message-ID: <20171211152219.GL2272@kib.kiev.ua> References: <201712110432.vBB4WbnE021090@repo.freebsd.org> <201712111509.vBBF9Aha081695@pdx.rh.CN85.dnsmgr.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201712111509.vBBF9Aha081695@pdx.rh.CN85.dnsmgr.net> User-Agent: Mutt/1.9.1 (2017-09-22) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.25 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 11 Dec 2017 15:22:28 -0000 On Mon, Dec 11, 2017 at 07:09:10AM -0800, Rodney W. Grimes wrote: > The current comment about a pcb, I thought that code was changed > so we only put the pointer to a pcb on the stack. pcb is on top of the stack, followed by the userspace FPU registers save area. I do not see any sense in existence of pcb in modern kernel, it is a remnant of the user area that was swappable. Currently pcb is swappable as well, but the value of this is much less then the overhead we pay by the stack space reduction. FPU save area is the on of the problem which makes us increase the amd64 stack size, AVX or even AVX512 make the things much worse. It is unlikely that somebody would run 32bit kernel on machine capable of that extensions, i.e. Haswell or Skylake.