On Tue, Feb 09, 2021 at 02:16:46PM -0800, Nadav Amit wrote: > From: Nadav Amit <na...@vmware.com> > > Currently, on_each_cpu() and similar functions do not exploit the > potential of concurrency: the function is first executed remotely and > only then it is executed locally. Functions such as TLB flush can take > considerable time, so this provides an opportunity for performance > optimization. > > To do so, modify smp_call_function_many_cond(), to allows the callers to > provide a function that should be executed (remotely/locally), and run > them concurrently. Keep other smp_call_function_many() semantic as it is > today for backward compatibility: the called function is not executed in > this case locally. > > smp_call_function_many_cond() does not use the optimized version for a > single remote target that smp_call_function_single() implements. For > synchronous function call, smp_call_function_single() keeps a > call_single_data (which is used for synchronization) on the stack. > Interestingly, it seems that not using this optimization provides > greater performance improvements (greater speedup with a single remote > target than with multiple ones). Presumably, holding data structures > that are intended for synchronization on the stack can introduce > overheads due to TLB misses and false-sharing when the stack is used for > other purposes. > > Reviewed-by: Dave Hansen <dave.han...@linux.intel.com> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: Rik van Riel <r...@surriel.com> > Cc: Thomas Gleixner <t...@linutronix.de> > Cc: Andy Lutomirski <l...@kernel.org> > Cc: Josh Poimboeuf <jpoim...@redhat.com> > Signed-off-by: Nadav Amit <na...@vmware.com>
Kernel-CI is giving me a regression that's most likely this patch: https://kernelci.org/test/case/id/602bdd621c979f83faaddcc6/ I'm not sure I can explain it yet. It did get me looking at on_each_cpu() and it appears that wants to be converted too, something like the below perhaps. --- a/kernel/smp.c +++ b/kernel/smp.c @@ -848,14 +848,7 @@ void __init smp_init(void) */ void on_each_cpu(smp_call_func_t func, void *info, int wait) { - unsigned long flags; - - preempt_disable(); - smp_call_function(func, info, wait); - local_irq_save(flags); - func(info); - local_irq_restore(flags); - preempt_enable(); + on_each_cpu_mask(cpu_online_mask, func, info, wait); } EXPORT_SYMBOL(on_each_cpu); @@ -878,15 +871,7 @@ EXPORT_SYMBOL(on_each_cpu); void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func, void *info, bool wait) { - unsigned int scf_flags; - - scf_flags = SCF_RUN_LOCAL; - if (wait) - scf_flags |= SCF_WAIT; - - preempt_disable(); - smp_call_function_many_cond(mask, func, info, scf_flags, NULL); - preempt_enable(); + on_each_cpu_cond_mask(NULL, func, info, wait, mask); } EXPORT_SYMBOL(on_each_cpu_mask); @@ -912,6 +897,13 @@ EXPORT_SYMBOL(on_each_cpu_mask); * You must not call this function with disabled interrupts or * from a hardware interrupt handler or from a bottom half handler. */ +void on_each_cpu_cond(smp_cond_func_t cond_func, smp_call_func_t func, + void *info, bool wait) +{ + on_each_cpu_cond_mask(cond_func, func, info, wait, cpu_online_mask); +} +EXPORT_SYMBOL(on_each_cpu_cond); + void on_each_cpu_cond_mask(smp_cond_func_t cond_func, smp_call_func_t func, void *info, bool wait, const struct cpumask *mask) { @@ -926,13 +918,6 @@ void on_each_cpu_cond_mask(smp_cond_func } EXPORT_SYMBOL(on_each_cpu_cond_mask); -void on_each_cpu_cond(smp_cond_func_t cond_func, smp_call_func_t func, - void *info, bool wait) -{ - on_each_cpu_cond_mask(cond_func, func, info, wait, cpu_online_mask); -} -EXPORT_SYMBOL(on_each_cpu_cond); - static void do_nothing(void *unused) { } ~
