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[110.174.173.27]) by smtp.gmail.com with ESMTPSA id q4sm3208683pjq.36.2020.07.23.07.09.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jul 2020 07:09:54 -0700 (PDT) Date: Fri, 24 Jul 2020 00:09:48 +1000 From: Nicholas Piggin Subject: Re: [PATCH v3 5/6] powerpc/pseries: implement paravirt qspinlocks for SPLPAR To: linuxppc-dev@lists.ozlabs.org, Michael Ellerman References: <20200706043540.1563616-1-npiggin@gmail.com> <20200706043540.1563616-6-npiggin@gmail.com> <874kqhvu1v.fsf@mpe.ellerman.id.au> In-Reply-To: <874kqhvu1v.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Message-Id: <1595512823.5k2rrd4zk5.astroid@bobo.none> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Peter Zijlstra , Boqun Feng , linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, virtualization@lists.linux-foundation.org, Ingo Molnar , Waiman Long , Will Deacon Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Excerpts from Michael Ellerman's message of July 9, 2020 8:53 pm: > Nicholas Piggin writes: >=20 >> Signed-off-by: Nicholas Piggin >> --- >> arch/powerpc/include/asm/paravirt.h | 28 ++++++++ >> arch/powerpc/include/asm/qspinlock.h | 66 +++++++++++++++++++ >> arch/powerpc/include/asm/qspinlock_paravirt.h | 7 ++ >> arch/powerpc/platforms/pseries/Kconfig | 5 ++ >> arch/powerpc/platforms/pseries/setup.c | 6 +- >> include/asm-generic/qspinlock.h | 2 + >=20 > Another ack? >=20 >> diff --git a/arch/powerpc/include/asm/paravirt.h b/arch/powerpc/include/= asm/paravirt.h >> index 7a8546660a63..f2d51f929cf5 100644 >> --- a/arch/powerpc/include/asm/paravirt.h >> +++ b/arch/powerpc/include/asm/paravirt.h >> @@ -45,6 +55,19 @@ static inline void yield_to_preempted(int cpu, u32 yi= eld_count) >> { >> ___bad_yield_to_preempted(); /* This would be a bug */ >> } >> + >> +extern void ___bad_yield_to_any(void); >> +static inline void yield_to_any(void) >> +{ >> + ___bad_yield_to_any(); /* This would be a bug */ >> +} >=20 > Why do we do that rather than just not defining yield_to_any() at all > and letting the build fail on that? >=20 > There's a condition somewhere that we know will false at compile time > and drop the call before linking? Mainly so you could use it in if (IS_ENABLED()) blocks, but would still catch the (presumably buggy) case where something calls it without the option set. I think I had it arranged a different way that was using IS_ENABLED=20 earlier and changed it but might as well keep it this way. >=20 >> diff --git a/arch/powerpc/include/asm/qspinlock_paravirt.h b/arch/powerp= c/include/asm/qspinlock_paravirt.h >> new file mode 100644 >> index 000000000000..750d1b5e0202 >> --- /dev/null >> +++ b/arch/powerpc/include/asm/qspinlock_paravirt.h >> @@ -0,0 +1,7 @@ >> +/* SPDX-License-Identifier: GPL-2.0-or-later */ >> +#ifndef __ASM_QSPINLOCK_PARAVIRT_H >> +#define __ASM_QSPINLOCK_PARAVIRT_H >=20 > _ASM_POWERPC_QSPINLOCK_PARAVIRT_H please. >=20 >> + >> +EXPORT_SYMBOL(__pv_queued_spin_unlock); >=20 > Why's that in a header? Should that (eventually) go with the generic impl= ementation? Yeah the qspinlock_paravirt.h header is a bit weird and only gets=20 included into kernel/locking/qspinlock.c >> diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platf= orms/pseries/Kconfig >> index 24c18362e5ea..756e727b383f 100644 >> --- a/arch/powerpc/platforms/pseries/Kconfig >> +++ b/arch/powerpc/platforms/pseries/Kconfig >> @@ -25,9 +25,14 @@ config PPC_PSERIES >> select SWIOTLB >> default y >> =20 >> +config PARAVIRT_SPINLOCKS >> + bool >> + default n >=20 > default n is the default. >=20 >> diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platf= orms/pseries/setup.c >> index 2db8469e475f..747a203d9453 100644 >> --- a/arch/powerpc/platforms/pseries/setup.c >> +++ b/arch/powerpc/platforms/pseries/setup.c >> @@ -771,8 +771,12 @@ static void __init pSeries_setup_arch(void) >> if (firmware_has_feature(FW_FEATURE_LPAR)) { >> vpa_init(boot_cpuid); >> =20 >> - if (lppaca_shared_proc(get_lppaca())) >> + if (lppaca_shared_proc(get_lppaca())) { >> static_branch_enable(&shared_processor); >> +#ifdef CONFIG_PARAVIRT_SPINLOCKS >> + pv_spinlocks_init(); >> +#endif >> + } >=20 > We could avoid the ifdef with this I think? Yes I think so. Thanks, Nick