From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH] tsc: use kvmclock for calibration Date: Thu, 09 Aug 2012 17:20:11 +0300 Message-ID: <5023C71B.6090707@redhat.com> References: <1344513463-7329-1-git-send-email-kraxel@redhat.com> <5023B2C4.90302@redhat.com> <5023C1D2.5090103@redhat.com> <5023C2BE.5070702@redhat.com> <5023C6B8.4090805@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: seabios@seabios.org, kvm@vger.kernel.org To: Gerd Hoffmann Return-path: In-Reply-To: <5023C6B8.4090805@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: seabios-bounces+gcbcs-seabios=m.gmane.org@seabios.org Sender: seabios-bounces+gcbcs-seabios=m.gmane.org@seabios.org List-Id: kvm.vger.kernel.org On 08/09/2012 05:18 PM, Gerd Hoffmann wrote: > Hi, > >>> So what do you suggest? The options I see are: >>> >>> (1) Use this patch (with alignment issue fixed of course). >>> (2) Do a full kvmclock implementation. Feels a bit like overkill. >>> (3) SeaBIOS can fallback to the PIT for timing on machines which >>> have no TSC. We could do that too in case we detect kvm ... >> >> What sort of timeouts are these? If seconds, maybe the rtc would be best. > > All sorts of timeouts, from a few miliseconds to seconds. > > The problematic ones are the longer timeouts, which wait for I/O stuff > like disk reads complete. The stuff with smaller timeouts (like waiting > for AHCI link become ready) tend to finish instantly in kvm. That's not guaranteed. The AHCI adapter might be real hardware. Or the emulation may change. What's wrong with having a full kvmclock implementation? Instead of issuing rdtsc call a function pointer. -- error compiling committee.c: too many arguments to function