From owner-freebsd-current@FreeBSD.ORG Wed May 18 16:52:45 2011 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 6C911106566C; Wed, 18 May 2011 16:52:45 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: from mail-vw0-f54.google.com (mail-vw0-f54.google.com [209.85.212.54]) by mx1.freebsd.org (Postfix) with ESMTP id E0CDF8FC12; Wed, 18 May 2011 16:52:44 +0000 (UTC) Received: by vws18 with SMTP id 18so1708612vws.13 for ; Wed, 18 May 2011 09:52:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; bh=EhXRXlZ8nSay9Px+S38WHZyx8P+G4wR7rNXw26tOz1E=; b=sdIYad8c4hnPB72fXZmiiR8yG4phec9M6rEzAjme+UQAC7/54xxD4dOS9z8rk23VcL daUsbpW0FjTTQwq5xT8Fbkv1FJ3yIW0ylNjfldU9Vs308LEijWTIe/dMiuPw2DfvuPHx qtYHXqtH5Yf0ha1l9JYyjlhuFtWB5frIMXej8= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; b=hWlSTEXxuAUD56bM77uyDn028PJ+r4NkSNRnnY6BPR5Enc7Fbkh+Lldc6bxKRTOePi QQAfuUxYtEAHCXX8AhhB0OO+pWRC15uegY1fGltB0PS39Hh0ipvgCrKcxpEhKZurmhCQ d71B4UaySJZzjJfQHltA2FUIptwYxzbVZ53YI= MIME-Version: 1.0 Received: by 10.220.42.74 with SMTP id r10mr621813vce.132.1305737563927; Wed, 18 May 2011 09:52:43 -0700 (PDT) Sender: asmrookie@gmail.com Received: by 10.220.201.3 with HTTP; Wed, 18 May 2011 09:52:43 -0700 (PDT) In-Reply-To: References: <4DD3F662.9040603@FreeBSD.org> Date: Wed, 18 May 2011 12:52:43 -0400 X-Google-Sender-Auth: asD9RAhrk3Z7Osbh5T6nMVum8Cg Message-ID: From: Attilio Rao To: Garrett Cooper Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Cc: freebsd-current@freebsd.org, Andriy Gapon , freebsd-arch@freebsd.org Subject: Re: [rfc] remove hlt_cpus et al sysctls and related code X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 18 May 2011 16:52:45 -0000 2011/5/18 Attilio Rao : > 2011/5/18 Garrett Cooper : >> On Wed, May 18, 2011 at 9:40 AM, Andriy Gapon wrote: >>> >>> I think that it is a well known fact that currently we do not have any = support for >>> dynamically offlining processors. =C2=A0Yet, we have some code that loo= ks like it does >>> provide that support and even provides a user interface to supposedly d= o that. >>> >>> What we don't currently do specifically: >>> - rebinding interrupts away from an offlined processor >>> - updating relevant cpu sets and masks >>> - protecting the above for concurrent access >>> - moving threads away from an offlined processor >>> - notifying potentially interested parties >>> - maybe more... >>> >>> The code has been in this shape for a long while and I would dare to sa= y that it >>> never really worked, not in "production ready" sense anyway. >>> An example of troubles caused by using that code can be found e.g. in t= he >>> followups to the following PR: >>> http://www.freebsd.org/cgi/query-pr.cgi?pr=3D145385 >>> And also discussed here: >>> http://thread.gmane.org/gmane.os.freebsd.stable/74462/focus=3D74510 >>> >>> I think that there already have been a proposal to remove the systcls a= nd the >>> code. =C2=A0I would like to re-submit that proposal. >>> Removing that code would: >>> 1) prevent users from hurting themselves by executing broken code >>> 2) potentially make things easier for largeSMP project >>> >>> Once we grow correct code for offlining CPUs, then we could re-introduc= e the >>> sysctls without any problems. >>> While the offlining code doesn't seem terribly hard to develop, it's a = big piece >>> of work and requires time and effort. >> >> =C2=A0 =C2=A0What would be nice too (even though it might not be possibl= e) is >> to make this more MI than it is today (i.e. sysctls that work for >> amd64, sparc64, etc), but that might be a pipe dream. >> Thanks! >> -Garrett > > That is actually the purpose. =C2=A0We should have a real online/offline > system for hotplugging CPUs, not only tied to x86 hyperthreading. > The htt specific parts are mostly hacks that don't take into account > all the necessary handover for it. For instance, I always promised to implement them and I never did, mostly because it is quite a bit of work in my idea and we don't really have a big pressure for it and there are really bigger things on my plate. If someone wants to step up and implementing offline/online CPUs I would be glad to discuss approaches I have in mind and help formalizing a plan for it, thus offering guidance for the implementation. Attilio --=20 Peace can only be achieved by understanding - A. Einstein