From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH v2 14/21] qemu-kvm: Rework VCPU state writeback API Date: Sun, 07 Feb 2010 14:51:19 +0100 Message-ID: <4B6EC557.9090804@web.de> References: <4822161334c3e10d7772dbd08dafdd3a78c86ce4.1265187223.git.jan.kiszka@siemens.com> <4B6EC180.7000203@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigFF91FAAEDB429A187D81E745" Cc: Marcelo Tosatti , kvm@vger.kernel.org, Anthony Liguori , Alexander Graf , Glauber Costa , qemu-devel@nongnu.org To: Avi Kivity Return-path: Received: from fmmailgate01.web.de ([217.72.192.221]:38638 "EHLO fmmailgate01.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751141Ab0BGNva (ORCPT ); Sun, 7 Feb 2010 08:51:30 -0500 In-Reply-To: <4B6EC180.7000203@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigFF91FAAEDB429A187D81E745 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Avi Kivity wrote: > On 02/03/2010 10:53 AM, Jan Kiszka wrote: >> This grand cleanup drops all reset and vmsave/load related >> synchronization points in favor of four(!) generic hooks: >> >> - cpu_synchronize_all_states in qemu_savevm_state_complete >> (initial sync from kernel before vmsave) >> - cpu_synchronize_all_post_init in qemu_loadvm_state >> (writeback after vmload) >> - cpu_synchronize_all_post_init in main after machine init >> - cpu_synchronize_all_post_reset in qemu_system_reset >> (writeback after system reset) >> >> These writeback points + the existing one of VCPU exec after >> cpu_synchronize_state map on three levels of writeback: >> >> - KVM_PUT_ASYNC_STATE (during runtime, other VCPUs continue to run) >> =20 >=20 > Wouldn't that be SYNC_STATE (state that is modified by the current vcpu= > only)? It's async /wrt other VCPUs. They continue to run and may interact with this VCPU while updating its state. >=20 >> - KVM_PUT_RESET_STATE (on synchronous system reset, all VCPUs stopped)= >> - KVM_PUT_FULL_STATE (on init or vmload, all VCPUs stopped as well) >> >> This level is passed to the arch-specific VCPU state writing function >> that will decide which concrete substates need to be written. That way= , >> no writer of load, save or reset functions that interact with in-kerne= l >> KVM states will ever have to worry about synchronization again. That >> also means that a lot of reasons for races, segfaults and deadlocks ar= e >> eliminated. >> >> cpu_synchronize_state remains untouched, just as Anthony suggested. We= >> continue to need it before reading or writing of VCPU states that are >> also tracked by in-kernel KVM subsystems. >> >> Consequently, this patch removes many cpu_synchronize_state calls that= >> are now redundant, just like remaining explicit register syncs. It doe= s >> not touch qemu-kvm's special hooks for mpstate, vcpu_events, or tsc >> loading. They will be cleaned up by individual patches. >> >> =20 >=20 > I'm uneasy about this. What are the rules for putting > cpu_synchronize_state() now? As before for code that accesses the state during runtime: Before you read or write some bit of it, call cpu_synchronize_state(). Only reset and save/restore handlers do not have to worry about synchronization anymore. It makes no sense to overload them with arch-specific KVM knowledge about what shall be written and when. Jan --------------enigFF91FAAEDB429A187D81E745 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org iEYEARECAAYFAktuxVsACgkQitSsb3rl5xSnSQCgt0XgUxAzUhgtmQhz3bMqsvUf 9+EAoKuKcP6VoL5Fb3O8rIW7FoUTJKcw =SKSm -----END PGP SIGNATURE----- --------------enigFF91FAAEDB429A187D81E745--