From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: + stupid-hack-to-make-mainline-build.patch added to -mm tree Date: Wed, 07 Mar 2007 02:22:50 +0100 Message-ID: <1173230571.24738.534.camel@localhost.localdomain> References: <200703060654.l266sVxr014860@shell0.pdx.osdl.net> <45ED16D2.3000202@vmware.com> <20070306084258.GA15745@elte.hu> <20070306084647.GA16280@elte.hu> <45ED2C82.3080008@vmware.com> <1173178774.24738.311.camel@localhost.localdomain> <45EDD82F.90204@vmware.com> <1173225182.24738.507.camel@localhost.localdomain> <45EE0A68.6010406@vmware.com> Reply-To: tglx@linutronix.de Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <45EE0A68.6010406@vmware.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.osdl.org Errors-To: virtualization-bounces@lists.osdl.org To: Dan Hecht Cc: Virtualization Mailing List , john stultz , LKML , Ingo Molnar , akpm@linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Tue, 2007-03-06 at 16:42 -0800, Dan Hecht wrote: > >> accounting would be wrong. Instead, we should allow the = > >> tick_sched_timer in cases (c) and (d) to have runtime configurable = > >> period, and then scale the time value accordingly before passing to = > >> account_system_time. This is probably something the Xen folks will wa= nt = > >> also, since I think Xen itself only gets 100hz hard timer, and so it c= an = > >> implement at best a oneshot virtual timer with 100hz resolution. Any = > >> objections to us doing something like this? > > = > > Yes. It's gross hackery. = > > = > > 1) We want to have a cleanup of the tick assumptions _all_ over the > > place and this is going to be real hard work. > > = > > 2) As I said above. The time accounting for virtualization needs to be > > fixed in a generic way. > > = > > I'm not going to accept some weird hackery for virtualization, which is > > of exactly ZERO value for the kernel itself. Quite the contrary it will > > make the cleanup harder and introduce another hard to remove thing, > > which will in the worst case last for ever. > > > = > Okay, to confirm I'm on the same page as you, you want to move process = > time accounting from being periodic sampled based to being trace based? = > i.e. at the system-call/interrupt boundaries, read clocksource and = > compute directly the amount of system/user/process time? At least for the paravirt guests this is the correct approach. Once the CPU vendors come up with a sane solution for a reliable and fast clock source we might use that on real hardware as well. > Do you know if anyone has explored this? I thought there was a = > discussion about this a while back but it was rejected due to the = > sample-based approach having much lower overheads on high system call = > rate workloads. Yes, with todays hardware it is simply a PITA. PowerPC has some basic support for this though, IIRC. tglx