From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 1/3] include files for kvmclock Date: Sun, 11 Nov 2007 11:15:51 +0200 Message-ID: <4736C847.90000@qumranet.com> References: <11945615632624-git-send-email-gcosta@redhat.com> <11945615703593-git-send-email-gcosta@redhat.com> <47341C4A.30508@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: jeremy-TSDbQ3PG+2Y@public.gmane.org, hollisb-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org, kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Glauber de Oliveira Costa To: Gerd Hoffmann Return-path: In-Reply-To: <47341C4A.30508-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Gerd Hoffmann wrote: >> +/* >> + * Guest has page alignment and padding requirements. At the host, it will >> + * only lead to wasted space at the vcpu struct. For this reason, the struct >> + * is not anonymous >> + */ >> +union kvm_hv_clock { >> + struct kvm_hv_clock_s { >> + u64 tsc_mult; >> + u64 now_ns; >> + /* That's the wall clock, not the water closet */ >> + u64 wc_sec; >> + u64 last_tsc; >> + /* At first, we could use the tsc value as a marker, but Jeremy >> + * well noted that it will cause us locking problems in 32-bit >> + * sys, so we have a special version field */ >> + u32 version; >> + } fields; >> + char page_align[PAGE_SIZE]; >> +}; >> > > What is the point in using a whole page per vcpu? You probably don't > want struct kvm_hv_clock_s cross a page border. Is that the only reason > or are there other constrains too? > We don't even have the cross-page-boundary constraint. The real issue is that on i386 physical addresses are 64-bit while hypercall arguments are 32-bit. A page frame number is 32-bit and so poses no issues. I see two workarounds for this: - make the first hypercall argument a u64 rather than a long (using two registers on i386) - use an msr for registering the clock address The first is more general, while the second has the nice property of taking care of live migration automatically. > As the kvm clock looks quite simliar to what xen does, how about making > the structs binary-compatible or simply reuse the xen version (struct > vcpu_time_info in xen/interface/xen.h)? > If there are no technical issues, I have no objections. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/