From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Dan Magenheimer" Subject: RE: [PATCH 0/2] Improve hpet accuracy Date: Mon, 9 Jun 2008 14:48:37 -0600 Message-ID: <20080609144837187.00000002776@djm-pc> References: Reply-To: "dan.magenheimer@oracle.com" Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser , Dave Winchell Cc: xen-devel , Ben Guthro List-Id: xen-devel@lists.xenproject.org > At guest install time you ought to be able to tell whether the guest > will use hpet or not based on its version (RHELx, SLESy, Winz etc etc) > and decide whether missed-ticks accounting is required or not. Unfortunately this is not true on Linux, at least without gathering (and hardcoding) more information about the system. Whether hpet is used or not is dependent not only on the OS/version and hvm config parameters, but also on kernel command line parameters and even the underlying CPU. For example, on RHEL5u1, if the tsc is synchronized and the CPU is Intel, and no kernel parameters are chosen, tsc will be chosen as the default clocksource even if hpet is present. Ugly. That said, if Dave's patch achieves the stated accuracy on most versions of Linux (e.g. at least RHEL4+5, 32+64, smp+1p) for SOME set of parameters (which might be different on each Linux version), it would still be better than what we have now. The ideal solution, I think, would be for the default hvm settings to "do the right thing" for both Windows and Linux at least for the vast majority of configuration choices. I'm not sure this is possible, but it sure would be nice. Dan -----Original Message----- From: Keir Fraser [mailto:keir.fraser@eu.citrix.com] Sent: Monday, June 09, 2008 1:36 AM To: Dave Winchell; dan.magenheimer@oracle.com Cc: Ben Guthro; xen-devel Subject: Re: [Xen-devel] [PATCH 0/2] Improve hpet accuracy On 9/6/08 00:26, "Dave Winchell" wrote: > 4) config file parameters Hpet enabled. Timer_mode set to HVM_HPET_guest_computes_missed_ticks for all Linux guests and to HVM_HPET_guest_does_not_compute_missed_ticks for Windows 2k8-64 and Vista 64. 8 vcpus for Linux and 2 for Windows. These new HVM_HPET options seems a weird design choice. It appears that you= can only set these or one of the old options, so there's not actually any = independence between the mode used by vpt.c and the mode used by hpet.c. At= guest install time you ought to be able to tell whether the guest will use= hpet or not based on its version (RHELx, SLESy, Winz etc etc) and decide w= hether missed-ticks accounting is required or not. I'd be more agreeable to a partch that stripped out the physical hpet acces= ses (since you say they are not the reason for the improvement in accuracy)= , built hpet on top of vpt, and added the necessary extra mechanisms to dea= l with interrupt broadcasts into vpt.c. And which was split into more separ= ate pieces of mechanism. -- Keir