From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nicholas Piggin Date: Thu, 23 Jul 2020 14:09:48 +0000 Subject: Re: [PATCH v3 5/6] powerpc/pseries: implement paravirt qspinlocks for SPLPAR Message-Id: <1595512823.5k2rrd4zk5.astroid@bobo.none> List-Id: 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 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linuxppc-dev@lists.ozlabs.org, Michael Ellerman Cc: Anton Blanchard , Boqun Feng , kvm-ppc@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Waiman Long , Ingo Molnar , Peter Zijlstra , virtualization@lists.linux-foundation.org, Will Deacon Excerpts from Michael Ellerman's message of July 9, 2020 8:53 pm: > Nicholas Piggin writes: > >> 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 + > > Another ack? > >> 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 yield_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 */ >> +} > > Why do we do that rather than just not defining yield_to_any() at all > and letting the build fail on that? > > 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 earlier and changed it but might as well keep it this way. > >> diff --git a/arch/powerpc/include/asm/qspinlock_paravirt.h b/arch/powerpc/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 > > _ASM_POWERPC_QSPINLOCK_PARAVIRT_H please. > >> + >> +EXPORT_SYMBOL(__pv_queued_spin_unlock); > > Why's that in a header? Should that (eventually) go with the generic implementation? Yeah the qspinlock_paravirt.h header is a bit weird and only gets included into kernel/locking/qspinlock.c >> diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/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 >> >> +config PARAVIRT_SPINLOCKS >> + bool >> + default n > > default n is the default. > >> diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/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); >> >> - 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 >> + } > > We could avoid the ifdef with this I think? Yes I think so. Thanks, Nick