From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44601) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dCjCF-00070S-Dr for qemu-devel@nongnu.org; Mon, 22 May 2017 05:00:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dCjC9-0001pn-BV for qemu-devel@nongnu.org; Mon, 22 May 2017 05:00:11 -0400 Received: from 7.mo179.mail-out.ovh.net ([46.105.61.94]:35959) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dCjC8-0001nq-0W for qemu-devel@nongnu.org; Mon, 22 May 2017 05:00:05 -0400 Received: from player690.ha.ovh.net (b6.ovh.net [213.186.33.56]) by mo179.mail-out.ovh.net (Postfix) with ESMTP id 75F8D39B2D for ; Mon, 22 May 2017 11:00:00 +0200 (CEST) Date: Mon, 22 May 2017 10:59:50 +0200 From: Greg Kurz Message-ID: <20170522105950.4af008c1@bahia.lan> In-Reply-To: <20170522020413.GF30246@umbus.fritz.box> References: <149518991537.24289.6673616934370284758.stgit@bahia.lan> <149518994010.24289.12584852638589552255.stgit@bahia.lan> <20170522020413.GF30246@umbus.fritz.box> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; boundary="Sig_/3Cv3ch1r+_G7MhMwkOhxENb"; protocol="application/pgp-signature" Subject: Re: [Qemu-devel] [PATCH v2 3/4] target/ppc: consolidate CPU device-tree id computation in helper List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: qemu-ppc@nongnu.org, qemu-devel@nongnu.org, Laurent Vivier , Bharata B Rao , Cedric Le Goater --Sig_/3Cv3ch1r+_G7MhMwkOhxENb Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Mon, 22 May 2017 12:04:13 +1000 David Gibson wrote: > On Fri, May 19, 2017 at 12:32:20PM +0200, Greg Kurz wrote: > > For historical reasons, we compute CPU device-tree ids with a non-trivi= al > > logic. This patch consolidate the logic in a single helper to be used > > in various places where it is currently open-coded. > >=20 > > It is okay to get rid of DIV_ROUND_UP() because we're sure that the num= ber > > of threads per core in the guest cannot exceed the number of threads per > > core in the host. =20 >=20 > However, your new logic still gives different answers in some cases. > In particular when max_cpus is not a multiple of smp_threads. Which > is generally a bad idea, but allowed for older machine types for > compatibility. e.g. smp_threads=3D4, max_cpus=3D6 smt=3D8 >=20 > Old logic: > DIV_ROUND_UP(6 * 8, 4) > =3D =E2=8C=8848 / 4=E2=8C=89 =3D 12 >=20 > New logic gives: =E2=8C=8A6 / 4=E2=8C=8B * 8 + (6 % 4) > =3D 1 * 8 + 2 > =3D 10 >=20 I now realize this two formulas are hardly reconcilable... this probably means that this patch shouldn't try to consolidate the logic in hw/ppc/spapr.c with the one in target/ppc/translate_init.c. > In any case the DIV_ROUND_UP() isn't to handle the case where guest > threads-per-core is bigger than host threads-per-core, it's (IIRC) for > the case where guest threads-per-core is not a factor of host > threads-per-core. Again, a bad idea, but I think allowed in some old > cases. >=20 FWIW, DIV_ROUND_UP() comes from this commit: f303f117fec3 spapr: ensure we have at least one XICS server but I agree that this was a bad idea... > >=20 > > Signed-off-by: Greg Kurz > > --- > > hw/ppc/spapr.c | 6 ++---- > > target/ppc/cpu.h | 17 +++++++++++++++++ > > target/ppc/translate_init.c | 3 +-- > > 3 files changed, 20 insertions(+), 6 deletions(-) > >=20 > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c > > index 75e298b4c6be..1bb05a9a6b07 100644 > > --- a/hw/ppc/spapr.c > > +++ b/hw/ppc/spapr.c > > @@ -981,7 +981,6 @@ static void *spapr_build_fdt(sPAPRMachineState *spa= pr, > > void *fdt; > > sPAPRPHBState *phb; > > char *buf; > > - int smt =3D kvmppc_smt_threads(); > > =20 > > fdt =3D g_malloc0(FDT_MAX_SIZE); > > _FDT((fdt_create_empty_tree(fdt, FDT_MAX_SIZE))); > > @@ -1021,7 +1020,7 @@ static void *spapr_build_fdt(sPAPRMachineState *s= papr, > > _FDT(fdt_setprop_cell(fdt, 0, "#size-cells", 2)); > > =20 > > /* /interrupt controller */ > > - spapr_dt_xics(DIV_ROUND_UP(max_cpus * smt, smp_threads), fdt, PHAN= DLE_XICP); > > + spapr_dt_xics(ppc_cpu_dt_id_from_index(max_cpus), fdt, PHANDLE_XIC= P); > > =20 > > ret =3D spapr_populate_memory(spapr, fdt); > > if (ret < 0) { > > @@ -1977,7 +1976,6 @@ static void spapr_init_cpus(sPAPRMachineState *sp= apr) > > MachineState *machine =3D MACHINE(spapr); > > MachineClass *mc =3D MACHINE_GET_CLASS(machine); > > char *type =3D spapr_get_cpu_core_type(machine->cpu_model); > > - int smt =3D kvmppc_smt_threads(); > > const CPUArchIdList *possible_cpus; > > int boot_cores_nr =3D smp_cpus / smp_threads; > > int i; > > @@ -2014,7 +2012,7 @@ static void spapr_init_cpus(sPAPRMachineState *sp= apr) > > sPAPRDRConnector *drc =3D > > spapr_dr_connector_new(OBJECT(spapr), > > SPAPR_DR_CONNECTOR_TYPE_CPU, > > - (core_id / smp_threads) * smt); > > + ppc_cpu_dt_id_from_index(core_i= d)); > > =20 > > qemu_register_reset(spapr_drc_reset, drc); > > } > > diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h > > index 401e10e7dad8..47fe6c64698f 100644 > > --- a/target/ppc/cpu.h > > +++ b/target/ppc/cpu.h > > @@ -2529,4 +2529,21 @@ int ppc_get_vcpu_dt_id(PowerPCCPU *cpu); > > PowerPCCPU *ppc_get_vcpu_by_dt_id(int cpu_dt_id); > > =20 > > void ppc_maybe_bswap_register(CPUPPCState *env, uint8_t *mem_buf, int = len); > > + > > +#if !defined(CONFIG_USER_ONLY) > > +#include "sysemu/cpus.h" > > +#include "target/ppc/kvm_ppc.h" > > + > > +static inline int ppc_cpu_dt_id_from_index(int cpu_index) > > +{ > > + /* POWER HV support has an historical limitation that different th= reads > > + * on a single core cannot be in different guests at the same time= . In > > + * order to allow KVM to assign guest threads to host cores accord= ingly, > > + * CPU device tree ids are spaced by the number of threads per hos= t cores. > > + */ > > + return (cpu_index / smp_threads) * kvmppc_smt_threads() > > + + (cpu_index % smp_threads); > > +} > > +#endif > > + > > #endif /* PPC_CPU_H */ > > diff --git a/target/ppc/translate_init.c b/target/ppc/translate_init.c > > index 56a0ab22cfbe..837a9a496a65 100644 > > --- a/target/ppc/translate_init.c > > +++ b/target/ppc/translate_init.c > > @@ -9851,8 +9851,7 @@ static void ppc_cpu_realizefn(DeviceState *dev, E= rror **errp) > > } > > =20 > > #if !defined(CONFIG_USER_ONLY) > > - cpu->cpu_dt_id =3D (cs->cpu_index / smp_threads) * max_smt > > - + (cs->cpu_index % smp_threads); > > + cpu->cpu_dt_id =3D ppc_cpu_dt_id_from_index(cs->cpu_index); > > =20 > > if (kvm_enabled() && !kvm_vcpu_id_is_valid(cpu->cpu_dt_id)) { > > error_setg(errp, "Can't create CPU with id %d in KVM", cpu->cp= u_dt_id); > > =20 >=20 --Sig_/3Cv3ch1r+_G7MhMwkOhxENb Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iEYEARECAAYFAlkiqIYACgkQAvw66wEB28LgKQCeOeLs7FyDjdnHYv/0W4hU9qao hOkAoKRu60gNyoqAtmUblg68mg58y0y4 =O+Di -----END PGP SIGNATURE----- --Sig_/3Cv3ch1r+_G7MhMwkOhxENb--