From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934769AbcIVPRz (ORCPT ); Thu, 22 Sep 2016 11:17:55 -0400 Received: from mail-pa0-f68.google.com ([209.85.220.68]:34084 "EHLO mail-pa0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933991AbcIVPRx (ORCPT ); Thu, 22 Sep 2016 11:17:53 -0400 Date: Thu, 22 Sep 2016 23:17:16 +0800 From: Boqun Feng To: Pan Xinhui Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, peterz@infradead.org, mingo@redhat.com, paulmck@linux.vnet.ibm.com, waiman.long@hpe.com, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v7 4/6] powerpc: lib/locks.c: Add cpu yield/wake helper function Message-ID: <20160922151716.GA22004@tardis.cn.ibm.com> References: <1474277037-15200-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> <1474277037-15200-5-git-send-email-xinhui.pan@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="yrj/dFKFPuw6o+aM" Content-Disposition: inline In-Reply-To: <1474277037-15200-5-git-send-email-xinhui.pan@linux.vnet.ibm.com> User-Agent: Mutt/1.7.0 (2016-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --yrj/dFKFPuw6o+aM Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi Xinhui, On Mon, Sep 19, 2016 at 05:23:55AM -0400, Pan Xinhui wrote: > Add two corresponding helper functions to support pv-qspinlock. >=20 > For normal use, __spin_yield_cpu will confer current vcpu slices to the > target vcpu(say, a lock holder). If target vcpu is not specified or it > is in running state, such conferging to lpar happens or not depends. >=20 > Because hcall itself will introduce latency and a little overhead. And > we do NOT want to suffer any latency on some cases, e.g. in interrupt han= dler. > The second parameter *confer* can indicate such case. >=20 > __spin_wake_cpu is simpiler, it will wake up one vcpu regardless of its > current vcpu state. >=20 > Signed-off-by: Pan Xinhui > --- > arch/powerpc/include/asm/spinlock.h | 4 +++ > arch/powerpc/lib/locks.c | 59 +++++++++++++++++++++++++++++++= ++++++ > 2 files changed, 63 insertions(+) >=20 > diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/a= sm/spinlock.h > index 6aef8dd..abb6b0f 100644 > --- a/arch/powerpc/include/asm/spinlock.h > +++ b/arch/powerpc/include/asm/spinlock.h > @@ -56,9 +56,13 @@ > /* We only yield to the hypervisor if we are in shared processor mode */ > #define SHARED_PROCESSOR (lppaca_shared_proc(local_paca->lppaca_ptr)) > extern void __spin_yield(arch_spinlock_t *lock); > +extern void __spin_yield_cpu(int cpu, int confer); > +extern void __spin_wake_cpu(int cpu); > extern void __rw_yield(arch_rwlock_t *lock); > #else /* SPLPAR */ > #define __spin_yield(x) barrier() > +#define __spin_yield_cpu(x,y) barrier() > +#define __spin_wake_cpu(x) barrier() > #define __rw_yield(x) barrier() > #define SHARED_PROCESSOR 0 > #endif > diff --git a/arch/powerpc/lib/locks.c b/arch/powerpc/lib/locks.c > index 6574626..892df7d 100644 > --- a/arch/powerpc/lib/locks.c > +++ b/arch/powerpc/lib/locks.c > @@ -23,6 +23,65 @@ > #include > #include > =20 > +/* > + * confer our slices to a specified cpu and return. If it is already run= ning or > + * cpu is -1, then we will check confer. If confer is NULL, we will retu= rn > + * otherwise we confer our slices to lpar. > + */ > +void __spin_yield_cpu(int cpu, int confer) > +{ > + unsigned int holder_cpu =3D cpu, yield_count; > + You don't need @holder_cpu at all, do you? > + if (cpu =3D=3D -1) > + goto yield_to_lpar; > + > + BUG_ON(holder_cpu >=3D nr_cpu_ids); > + yield_count =3D be32_to_cpu(lppaca_of(holder_cpu).yield_count); > + > + /* if cpu is running, confer slices to lpar conditionally*/ > + if ((yield_count & 1) =3D=3D 0) > + goto yield_to_lpar; > + > + plpar_hcall_norets(H_CONFER, > + get_hard_smp_processor_id(holder_cpu), yield_count); > + return; > + > +yield_to_lpar: > + if (confer) > + plpar_hcall_norets(H_CONFER, -1, 0); > +} > +EXPORT_SYMBOL_GPL(__spin_yield_cpu); > + > +void __spin_wake_cpu(int cpu) > +{ > + unsigned int holder_cpu =3D cpu; > + Ditto. Regards, Boqun > + BUG_ON(holder_cpu >=3D nr_cpu_ids); > + /* > + * NOTE: we should always do this hcall regardless of > + * the yield_count of the holder_cpu. > + * as thers might be a case like below; > + * CPU 1 2 > + * yielded =3D true > + * if (yielded) > + * __spin_wake_cpu() > + * __spin_yield_cpu() > + * > + * So we might lose a wake if we check the yield_count and > + * return directly if the holder_cpu is running. > + * IOW. do NOT code like below. > + * yield_count =3D be32_to_cpu(lppaca_of(holder_cpu).yield_count); > + * if ((yield_count & 1) =3D=3D 0) > + * return; > + * > + * a PROD hcall marks the target_cpu proded, which cause the next cede = or confer > + * called on the target_cpu invalid. > + */ > + plpar_hcall_norets(H_PROD, > + get_hard_smp_processor_id(holder_cpu)); > +} > +EXPORT_SYMBOL_GPL(__spin_wake_cpu); > + > #ifndef CONFIG_QUEUED_SPINLOCKS > void __spin_yield(arch_spinlock_t *lock) > { > --=20 > 2.4.11 >=20 --yrj/dFKFPuw6o+aM Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEcBAABCAAGBQJX4/X4AAoJEEl56MO1B/q4y6gH/2AGxmEsj0HH4US1mcYUC7Qt jlvBMes+KDlso1yy+lG5M3U8dmfWVjiN+QHQq/XT7RSU9u69sY0mPzifrRhBt4eF Jir1MwKnW4VymB5gjbJakNNaCL48OpaGm4wBZFqkl+9y36Cb3v7ZuSIXtVLbQwmj oJt0baU46hGpGKcgAqhPthPqOkaZW/1z8ifW+tZWI84kR+AvstZXYfNgcWqvun7V rAddDUiPCoWImT7pzvyrllwp7bMAeezaAALlj5AxfVD6py4mcUfl4itjhT8b6J4v QbOwzHakp/UmLlMEairtDiLFglZTbCHY2dm+PCb2myqw1bsGKTdRAnGZIo5CV74= =y/qP -----END PGP SIGNATURE----- --yrj/dFKFPuw6o+aM--