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Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1pk9eT-00A4qm-13; Wed, 05 Apr 2023 20:22:47 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 3084B300202; Wed, 5 Apr 2023 22:22:40 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 18EDB27985545; Wed, 5 Apr 2023 22:22:40 +0200 (CEST) Date: Wed, 5 Apr 2023 22:22:40 +0200 From: Peter Zijlstra To: Ankur Arora Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, willy@infradead.org, mgorman@suse.de, rostedt@goodmis.org, tglx@linutronix.de, vincent.guittot@linaro.org, jon.grimm@amd.com, bharata@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com Subject: Re: [PATCH 8/9] irqentry: define irqentry_exit_allow_resched() Message-ID: <20230405202240.GE365912@hirez.programming.kicks-ass.net> References: <20230403052233.1880567-1-ankur.a.arora@oracle.com> <20230403052233.1880567-9-ankur.a.arora@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230403052233.1880567-9-ankur.a.arora@oracle.com> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 3374814000B X-Rspam-User: X-Stat-Signature: 3qgri36x9bm7samuzc38thiis8ynzp8o X-HE-Tag: 1680726183-456616 X-HE-Meta: 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 5ltxRVxf WYVp7CJZAb9KMv5LilftSyZBIfyqyyGods19Qcp6DP2DIcByjditpxDu59K3OBhbLEcrOtMgtib1uGTba6d/FxYfv+Bd4J2Tg3pQg6JPPuuCJPBOQS6jrPI0uMUdGGwmZZtNLP9YuEJ8xPhB2TsBaU0heDHH+sSf5851YwntMiGPz+fUXpmy3c9SLxW+vQA7kMKtbfdfR5SIqo0xpiZjyX59cN1jd4cVIYNF8 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Apr 02, 2023 at 10:22:32PM -0700, Ankur Arora wrote: > Allow threads marked TIF_ALLOW_RESCHED to be rescheduled in irqexit. > > This is only necessary under !preempt_model_preemptible() for which > we reuse the same logic as irqentry_exit_code_resched(). > > Signed-off-by: Ankur Arora > --- > kernel/entry/common.c | 8 ++++++++ > kernel/sched/core.c | 36 +++++++++++++++++++++--------------- > 2 files changed, 29 insertions(+), 15 deletions(-) > > diff --git a/kernel/entry/common.c b/kernel/entry/common.c > index be61332c66b5..f1005595ebe7 100644 > --- a/kernel/entry/common.c > +++ b/kernel/entry/common.c > @@ -390,6 +390,9 @@ void raw_irqentry_exit_cond_resched(void) > preempt_schedule_irq(); > } > } > + > +void irqentry_exit_allow_resched(void) __alias(raw_irqentry_exit_cond_resched); Because typing raw_irqentry_exit_cond_resched() was too much effort? > + > #ifdef CONFIG_PREEMPT_DYNAMIC > #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL) > DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched); > @@ -431,6 +434,11 @@ noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state) > instrumentation_begin(); > if (IS_ENABLED(CONFIG_PREEMPTION)) > irqentry_exit_cond_resched(); > + /* > + * We care about this clause only in the dynamic !preemptible case. > + */ > + if (unlikely(!preempt_model_preemptible() && resched_allowed())) > + irqentry_exit_allow_resched(); This is wrong, if we have dynamic preemption then we have CONFIG_PREEMPTION and we'll have that irqentry_exit_cond_resched() call. Basically what you've written above is something like: static_call(foo); // raw_foo() when A, NOP if !A if (!A) raw_foo(); And yeah, you've got the extra resched_allowed() thing in there, but that doesn't make it any better -- this is all quite horrible. What you really care about is the CONFIG_PREEMPTION=n case, but that you don't actually handle. > /* Covers both tracing and lockdep */ > trace_hardirqs_on(); > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 0d18c3969f90..11845a91b691 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -8597,28 +8599,32 @@ EXPORT_SYMBOL(__cond_resched_rwlock_write); > * SC:preempt_schedule > * SC:preempt_schedule_notrace > * SC:irqentry_exit_cond_resched > + * SC:irqentry_exit_allow_resched > * > * > * NONE: > - * cond_resched <- __cond_resched > - * might_resched <- RET0 > - * preempt_schedule <- NOP > - * preempt_schedule_notrace <- NOP > - * irqentry_exit_cond_resched <- NOP > + * cond_resched <- __cond_resched > + * might_resched <- RET0 > + * preempt_schedule <- NOP > + * preempt_schedule_notrace <- NOP > + * irqentry_exit_cond_resched <- NOP > + * irqentry_exit_allow_resched <- irqentry_exit_allow_resched > * > * VOLUNTARY: > - * cond_resched <- __cond_resched > - * might_resched <- __cond_resched > - * preempt_schedule <- NOP > - * preempt_schedule_notrace <- NOP > - * irqentry_exit_cond_resched <- NOP > + * cond_resched <- __cond_resched > + * might_resched <- __cond_resched > + * preempt_schedule <- NOP > + * preempt_schedule_notrace <- NOP > + * irqentry_exit_cond_resched <- NOP > + * irqentry_exit_allow_resched <- irqentry_exit_allow_resched > * > * FULL: > - * cond_resched <- RET0 > - * might_resched <- RET0 > - * preempt_schedule <- preempt_schedule > - * preempt_schedule_notrace <- preempt_schedule_notrace > - * irqentry_exit_cond_resched <- irqentry_exit_cond_resched > + * cond_resched <- RET0 > + * might_resched <- RET0 > + * preempt_schedule <- preempt_schedule > + * preempt_schedule_notrace <- preempt_schedule_notrace > + * irqentry_exit_cond_resched <- irqentry_exit_cond_resched > + * irqentry_exit_allow_resched <- NOP > */ This ^ is all complete nonsense.. irqentry_exit_allow_resched() is not a static call. It's an alias of raw_irqentry_exit_cond_resched which circumvents the static call entirely.