From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Date: Wed, 22 Mar 2023 23:14:28 +0000 Subject: Re: [PATCH v5 7/7] sched, smp: Trace smp callback causing an IPI Message-Id: <20230322231428.GV2017917@hirez.programming.kicks-ass.net> List-Id: References: <20230307143558.294354-1-vschneid@redhat.com> <20230307143558.294354-8-vschneid@redhat.com> <20230322095329.GS2017917@hirez.programming.kicks-ass.net> <20230322140434.GC2357380@hirez.programming.kicks-ass.net> <20230322172242.GH2357380@hirez.programming.kicks-ass.net> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Valentin Schneider Cc: linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, openrisc@lists.librecores.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, x86@kernel.org, "Paul E. McKenney" , Steven Rostedt , Thomas Gleixner , Sebastian Andrzej Siewior , Juri Lelli , Daniel Bristot de Oliveira , Marcelo Tosatti , Frederic Weisbecker , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Marc Zyngier , Mark Rutland , Russell King , Nicholas Piggin , Guo Ren , "David S. Miller" On Wed, Mar 22, 2023 at 06:22:28PM +0000, Valentin Schneider wrote: > On 22/03/23 18:22, Peter Zijlstra wrote: > >> hackbench-157 [001] 10.894320: ipi_send_cpu: cpu=3 callsite=check_preempt_curr+0x37 callback=0x0 > > > > Arguably we should be setting callback to scheduler_ipi(), except > > ofcourse, that's not an actual function... > > > > Maybe we can do "extern inline" for the actual users and provide a dummy > > function for the symbol when tracing. > > > > Huh, I wasn't aware that was an option, I'll look into that. I did scribble > down a comment next to smp_send_reschedule(), but having a decodable > function name would be better! So clang-15 builds the below (and generates the expected code), but gcc-12 vomits nonsense about a non-static inline calling a static inline or somesuch bollocks :-/ --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1991,7 +1991,7 @@ extern char *__get_task_comm(char *to, s }) #ifdef CONFIG_SMP -static __always_inline void scheduler_ipi(void) +extern __always_inline void scheduler_ipi(void) { /* * Fold TIF_NEED_RESCHED into the preempt_count; anybody setting --- a/include/linux/smp.h +++ b/include/linux/smp.h @@ -130,9 +130,9 @@ extern void arch_smp_send_reschedule(int * scheduler_ipi() is inline so can't be passed as callback reason, but the * callsite IP should be sufficient for root-causing IPIs sent from here. */ -#define smp_send_reschedule(cpu) ({ \ - trace_ipi_send_cpu(cpu, _RET_IP_, NULL); \ - arch_smp_send_reschedule(cpu); \ +#define smp_send_reschedule(cpu) ({ \ + trace_ipi_send_cpu(cpu, _RET_IP_, &scheduler_ipi); \ + arch_smp_send_reschedule(cpu); \ }) /* --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3790,6 +3790,15 @@ static int ttwu_runnable(struct task_str } #ifdef CONFIG_SMP +void scheduler_ipi(void) +{ + /* + * Actual users should end up using the extern inline, this is only + * here for the symbol. + */ + BUG(); +} + void sched_ttwu_pending(void *arg) { struct llist_node *llist = arg;