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Mon, 6 Jan 2025 05:19:34 +0000 (GMT) From: Shrikanth Hegde To: mpe@ellerman.id.au, maddy@linux.ibm.com, linuxppc-dev@lists.ozlabs.org Cc: sshegde@linux.ibm.com, npiggin@gmail.com, christophe.leroy@csgroup.eu, linux-kernel@vger.kernel.org Subject: [PATCH v3 1/1] powerpc: Enable dynamic preemption Date: Mon, 6 Jan 2025 10:49:19 +0530 Message-ID: <20250106051919.55020-2-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.43.5 In-Reply-To: <20250106051919.55020-1-sshegde@linux.ibm.com> References: <20250106051919.55020-1-sshegde@linux.ibm.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: o_U7VfXHwPN--Txs21H4QlPEAZ8Oy7cE X-Proofpoint-ORIG-GUID: fawtzZlIlkVx1dNJH43koXWzAN7hQQgr X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1051,Hydra:6.0.680,FMLib:17.12.62.30 definitions=2024-10-15_01,2024-10-11_01,2024-09-30_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 clxscore=1015 malwarescore=0 priorityscore=1501 bulkscore=0 spamscore=0 impostorscore=0 mlxlogscore=999 phishscore=0 suspectscore=0 mlxscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2411120000 definitions=main-2501060042 Once the lazy preemption is supported, it would be desirable to change the preemption models at runtime. So add support for dynamic preemption using DYNAMIC_KEY. In irq-exit to kernel path, use preempt_model_preemptible for decision. Other way would be using static key based decision. Keeping it simpler since key based change didn't show performance improvement. Also print the right preemption model in __die. ::Tested lightly on Power10 LPAR Performance numbers indicate that, preempt=none(no dynamic) and preempt=none(dynamic) are similar. cat /sys/kernel/debug/sched/preempt (none) voluntary full lazy perf stat -e probe:__cond_resched -a sleep 1 Performance counter stats for 'system wide': 1,253 probe:__cond_resched echo full > /sys/kernel/debug/sched/preempt cat /sys/kernel/debug/sched/preempt none voluntary (full) lazy perf stat -e probe:__cond_resched -a sleep 1 Performance counter stats for 'system wide': 0 probe:__cond_resched Signed-off-by: Shrikanth Hegde --- arch/powerpc/Kconfig | 1 + arch/powerpc/include/asm/preempt.h | 12 ++++++++++++ arch/powerpc/kernel/interrupt.c | 6 +++++- arch/powerpc/kernel/traps.c | 6 +++++- arch/powerpc/lib/vmx-helper.c | 2 +- 5 files changed, 24 insertions(+), 3 deletions(-) create mode 100644 arch/powerpc/include/asm/preempt.h diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index db9f7b2d07bf..b14218344e74 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -272,6 +272,7 @@ config PPC select HAVE_PERF_EVENTS_NMI if PPC64 select HAVE_PERF_REGS select HAVE_PERF_USER_STACK_DUMP + select HAVE_PREEMPT_DYNAMIC_KEY select HAVE_RETHOOK if KPROBES select HAVE_REGS_AND_STACK_ACCESS_API select HAVE_RELIABLE_STACKTRACE diff --git a/arch/powerpc/include/asm/preempt.h b/arch/powerpc/include/asm/preempt.h new file mode 100644 index 000000000000..eb1ed8295f13 --- /dev/null +++ b/arch/powerpc/include/asm/preempt.h @@ -0,0 +1,12 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __ASM_POWERPC_PREEMPT_H +#define __ASM_POWERPC_PREEMPT_H + +#include + +#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY) +#include +DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched); +#endif + +#endif /* __ASM_POWERPC_PREEMPT_H */ diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c index 8f4acc55407b..8e2400ba208c 100644 --- a/arch/powerpc/kernel/interrupt.c +++ b/arch/powerpc/kernel/interrupt.c @@ -25,6 +25,10 @@ unsigned long global_dbcr0[NR_CPUS]; #endif +#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY) +DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched); +#endif + #ifdef CONFIG_PPC_BOOK3S_64 DEFINE_STATIC_KEY_FALSE(interrupt_exit_not_reentrant); static inline bool exit_must_hard_disable(void) @@ -396,7 +400,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs) /* Returning to a kernel context with local irqs enabled. */ WARN_ON_ONCE(!(regs->msr & MSR_EE)); again: - if (IS_ENABLED(CONFIG_PREEMPTION)) { + if (preempt_model_preemptible()) { /* Return to preemptible kernel context */ if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) { if (preempt_count() == 0) diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c index edf5cabe5dfd..2556fa8ec019 100644 --- a/arch/powerpc/kernel/traps.c +++ b/arch/powerpc/kernel/traps.c @@ -266,7 +266,11 @@ static int __die(const char *str, struct pt_regs *regs, long err) printk("%s PAGE_SIZE=%luK%s%s%s%s%s%s %s\n", IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN) ? "LE" : "BE", PAGE_SIZE / 1024, get_mmu_str(), - IS_ENABLED(CONFIG_PREEMPT) ? " PREEMPT" : "", + preempt_model_none() ? "none" : + preempt_model_voluntary() ? "voluntary" : + preempt_model_full() ? "full" : + preempt_model_lazy() ? "lazy" : + "", IS_ENABLED(CONFIG_SMP) ? " SMP" : "", IS_ENABLED(CONFIG_SMP) ? (" NR_CPUS=" __stringify(NR_CPUS)) : "", debug_pagealloc_enabled() ? " DEBUG_PAGEALLOC" : "", diff --git a/arch/powerpc/lib/vmx-helper.c b/arch/powerpc/lib/vmx-helper.c index 58ed6bd613a6..7b069c832ce2 100644 --- a/arch/powerpc/lib/vmx-helper.c +++ b/arch/powerpc/lib/vmx-helper.c @@ -45,7 +45,7 @@ int exit_vmx_usercopy(void) * set and we are preemptible. The hack here is to schedule a * decrementer to fire here and reschedule for us if necessary. */ - if (IS_ENABLED(CONFIG_PREEMPTION) && need_resched()) + if (preempt_model_preemptible() && need_resched()) set_dec(1); return 0; } -- 2.39.3