From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60451) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dsBE7-0008Mg-8r for qemu-devel@nongnu.org; Wed, 13 Sep 2017 13:13:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dsBE2-0002d4-Rw for qemu-devel@nongnu.org; Wed, 13 Sep 2017 13:13:27 -0400 Received: from 8.mo2.mail-out.ovh.net ([188.165.52.147]:38212) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dsBE2-0002bn-MY for qemu-devel@nongnu.org; Wed, 13 Sep 2017 13:13:22 -0400 Received: from player770.ha.ovh.net (b6.ovh.net [213.186.33.56]) by mo2.mail-out.ovh.net (Postfix) with ESMTP id 082E6AB885 for ; Wed, 13 Sep 2017 19:13:20 +0200 (CEST) Date: Wed, 13 Sep 2017 19:13:09 +0200 From: Greg Kurz Message-ID: <20170913191309.56bf8fa4@bahia.lan> In-Reply-To: <760c3889-8561-9bce-e565-ccbcb9eb8cf5@ilande.co.uk> References: <1505054255-2990-1-git-send-email-mark.cave-ayland@ilande.co.uk> <1505054255-2990-3-git-send-email-mark.cave-ayland@ilande.co.uk> <20170911095059.101e0cfc@bahia.lan> <20170911093032.GA2857@work-vm> <20170911104854.GB2784@umbus.fritz.box> <20170912162100.GD2225@work-vm> <1bb6a27d-89a5-2e70-6976-74ab24430ec4@ilande.co.uk> <4f0cb74a-ae00-5921-291c-49c9acdb3e02@ilande.co.uk> <20170913060203.GG7550@umbus.fritz.box> <760c3889-8561-9bce-e565-ccbcb9eb8cf5@ilande.co.uk> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; boundary="Sig_/r2DfEmTwgnTsuI+k8=Sllkv"; protocol="application/pgp-signature" Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH 2/4] ppc: add CPU IRQ state to PPC VMStateDescription List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Mark Cave-Ayland Cc: David Gibson , Alexey Kardashevskiy , lvivier@redhat.com, qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , qemu-ppc@nongnu.org --Sig_/r2DfEmTwgnTsuI+k8=Sllkv Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Wed, 13 Sep 2017 17:44:54 +0100 Mark Cave-Ayland wrote: > On 13/09/17 07:02, David Gibson wrote: >=20 > >>> Alexey - do you recall from your analysis why these fields were no > >>> longer deemed necessary, and how your TCG tests were configured? =20 > >> > >> I most certainly did not do analysis (my bad. sorry) - I took the patch > >> from David as he left the team, fixed to compile and pushed away. I am= also > >> very suspicions we did not try migrating TCG or anything but pseries. = My > >> guest that things did not break (if they did not which I am not sure a= bout, > >> for the TCG case) because the interrupt controller (XICS) or the > >> pseries-guest took care of resending an interrupt which does not seem = to be > >> the case for mac99. =20 > >=20 > > Right, that's probably true. The main point, though, is that these > > fields were dropped a *long* time ago, when migration was barely > > working to begin with. In particular I'm pretty sure most of the > > non-pseries platforms were already pretty broken for migration > > (amongst other things). > >=20 > > Polishing the mac platforms up to working again, including migration, > > is a reasonable goal. But it can't be at the expense of pseries, > > which is already working, used in production, and much better tested > > than mac99 or g3beige ever were. =20 >=20 > Oh I completely agree since I'm well aware pseries likely has more users > than the Mac machines - my question was directed more about why we > support backwards migration. >=20 Downstream support backward migration because end users/customers ask for it for maximum flexibility when it comes to move workloads around different sy= stems with different QEMU versions. This is fairly usual in data centers with many systems. As others already said, breaking things upstream may turn downstream work into a nightmare (and FWIW, most of the people working on ppc are also involved in downstream work). Cheers, -- Greg > I spent several hours yesterday poking my Darwin test case with trying > the different combinations of pending_interrupts, irq_input_state and > access_type and could easily provoke migration failures unless all 3 of > the fields were present so a practical test shows they are still > required for TCG migration. I think ppc_set_irq()'s use of the interrupt > fields in hw/ppc/ppc.c and the subsequent reference to pending > interrupts in target/ppc may explain why I see freezes/hangs until a key > is pressed in many cases. >=20 >=20 > ATB, >=20 > Mark. --Sig_/r2DfEmTwgnTsuI+k8=Sllkv Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- iF0EARECAB0WIQQr1DtEU17Ap5iU26IC/DrrAQHbwgUCWblnJQAKCRAC/DrrAQHb wjHbAJsH7P1LWYJVaXNUtvyv1aDLUajmXACggCB2VIXKSbh05tDNrDZhn02GjpY= =K8Xq -----END PGP SIGNATURE----- --Sig_/r2DfEmTwgnTsuI+k8=Sllkv--