From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52086) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bLQMX-0006nH-7j for qemu-devel@nongnu.org; Fri, 08 Jul 2016 03:38:14 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bLQMR-00040V-UQ for qemu-devel@nongnu.org; Fri, 08 Jul 2016 03:38:12 -0400 Date: Fri, 8 Jul 2016 17:39:52 +1000 From: David Gibson Message-ID: <20160708073952.GQ14675@voom.fritz.box> References: <1467903025-13383-1-git-send-email-bharata@linux.vnet.ibm.com> <1467903025-13383-4-git-send-email-bharata@linux.vnet.ibm.com> <20160708052413.GM14675@voom.fritz.box> <20160708064112.GK25522@in.ibm.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="lYtTbTuCUQxZgETo" Content-Disposition: inline In-Reply-To: <20160708064112.GK25522@in.ibm.com> Subject: Re: [Qemu-devel] [RFC PATCH v2 3/5] spapr: Set stable_cpu_id for threads of CPU cores List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Bharata B Rao Cc: qemu-devel@nongnu.org, qemu-ppc@nongnu.org, imammedo@redhat.com, groug@kaod.org, nikunj@linux.vnet.ibm.com, pbonzini@redhat.com --lYtTbTuCUQxZgETo Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Jul 08, 2016 at 12:11:12PM +0530, Bharata B Rao wrote: > On Fri, Jul 08, 2016 at 03:24:13PM +1000, David Gibson wrote: > > On Thu, Jul 07, 2016 at 08:20:23PM +0530, Bharata B Rao wrote: > > > Conditonally set stable_cpu_id for CPU threads that are created as pa= rt > > > of spapr CPU cores. The use of stable_cpu_id is enabled for pseries-2= =2E7 > > > onwards. > > >=20 > > > Signed-off-by: Bharata B Rao > > > --- > > > hw/ppc/spapr_cpu_core.c | 7 +++++++ > > > 1 file changed, 7 insertions(+) > > >=20 > > > diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c > > > index b104778..0ec3513 100644 > > > --- a/hw/ppc/spapr_cpu_core.c > > > +++ b/hw/ppc/spapr_cpu_core.c > > > @@ -293,8 +293,15 @@ static void spapr_cpu_core_realize(DeviceState *= dev, Error **errp) > > > for (i =3D 0; i < cc->nr_threads; i++) { > > > char id[32]; > > > obj =3D sc->threads + i * size; > > > + CPUState *cs; > > > =20 > > > object_initialize(obj, size, typename); > > > + cs =3D CPU(obj); > > > + > > > + /* Use core_id (which is actually cpu_dt_id) as stable CPU i= d */ > > > + if (cs->has_stable_cpu_id) { > > > + cs->stable_cpu_id =3D cc->core_id + i; > > > + } > >=20 > > Testing cs->has_stable_cpu_id here in machine type specific code seems > > really weird. It's the machine type that knows whether it has a > > stable ID to give to the CPU or not, rather than the other way around. > >=20 > > Since we haven't yet had a release with cpu cores, I think the right > > thing is for cpu_core to unconditionally set the stable ID (and set > > has_stable_id to true). >=20 > Right, we can set cpu_stable_id unconditionally here since this code path > (core realize) will be taken only for pseries-2.7 onwards. has_stable_id > will get set as part of the property we defined in SPAPR_COMPAT_2_7. Hrm, that's true. But when you describe it like that it sounds like a really non-obvious and fragile dependency between different components. > > The backup path that does thread-based cpu > > init, can set has_stable_id to false (if that's not the default). >=20 > Default is off, but turning it on for 2.7 will be inherited by 2.6 > and others below. Hence I have code to explicitly disable this prop > for 2.6 and below via SPAPR_COMPAT_2_6. This is all seeming terribly awkward. Can we try investigating a different approach: 1. Rename cpu_index to cpu_id, but it's still used in the same places it's used. 2. Remove assumptions that cpu_id values are contiguous or dense =20 3. Machine type decides whether it wants to populate the cpu_id values explicitly, or leave it to generic code to calculate them as cpu_index is calculated now. 4. Ideally, generic code enforces that the machine type populates either all or none of the cpu_id values. Does that seem workable? --=20 David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson --lYtTbTuCUQxZgETo Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIbBAEBAgAGBQJXf1jIAAoJEGw4ysog2bOS+6MP+JcFrpvwRzRRyaMANf321Zvf YdwxgTZRtm6AAVxr2GEBk/3hvbwOrrDILMr9ahduEK9AdWWPpQRQka+A71KMuFMR ngGYSNaA/FMf+7WxJnYPKaI4u0idpDoRtgvO11LWgu42eVnDieDKhMv/gDtJyje6 UoJhZmxUDpprRUBGpj4UGACFrNr5A/xrdBGMAmC9u4YBZVtyXZmjBsgPCMgWWvpc +p1d4kaSK+eEqP3tUOrBxCNEYtUWDyPdBHIMR1L8sa17uopk+nAZtPGB/2+QLYW4 IhQioMVONAJLzJMKNyAXySeMGpIvfesalBnq0gba+Zl8zDyAaG3NFpe95nlZMbCg 15Du5KVI1saI4uJb2aqFugquyycT/+zoGNcnhVLAWfpvtA7HyGUv8y1Vrli3+q0W yF50bqfhA2Wauaohe3juzi8j8hhmLLHr4E1nXkVGtsC2YXdwFg38VqZ+k2OrbhBl MtSGBxzI6s7nHXMOuDC0Uon7V2Wyo+89Pi98Es7Y5UGqtFRxt7TBcnTSApCZMpXw cBGABNPQZRFkMOc0F2Oxm7XTH80MVcQkbNRO3wjgORcj0ozEUD++O/McjqkIbXSQ OLfJ/ohuZLjuyo4IuxJ/TZa/Oxx7LYZGWEXesFJga6hjyvyhr5XMtQZk5911Ai76 HZ7VavfzHompHXaJr10= =lUft -----END PGP SIGNATURE----- --lYtTbTuCUQxZgETo--