mirror of
https://github.com/torvalds/linux
synced 2024-11-05 18:23:50 +00:00
e950cca3f3
The check_preemption_disabled() function uses cpumask_equal() to see if the task is bounded to the current CPU only. cpumask_equal() calls memcmp() to do the comparison. As x86 doesn't have __HAVE_ARCH_MEMCMP, the slow memcmp() function in lib/string.c is used. On a RT kernel that call check_preemption_disabled() very frequently, below is the perf-record output of a certain microbenchmark: 42.75% 2.45% testpmd [kernel.kallsyms] [k] check_preemption_disabled 40.01% 39.97% testpmd [kernel.kallsyms] [k] memcmp We should avoid calling memcmp() in performance critical path. So the cpumask_equal() call is now replaced with an equivalent simpler check. Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Juri Lelli <juri.lelli@redhat.com> Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/20191003203608.21881-1-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
67 lines
1.4 KiB
C
67 lines
1.4 KiB
C
// SPDX-License-Identifier: GPL-2.0
|
|
/*
|
|
* lib/smp_processor_id.c
|
|
*
|
|
* DEBUG_PREEMPT variant of smp_processor_id().
|
|
*/
|
|
#include <linux/export.h>
|
|
#include <linux/kprobes.h>
|
|
#include <linux/sched.h>
|
|
|
|
notrace static nokprobe_inline
|
|
unsigned int check_preemption_disabled(const char *what1, const char *what2)
|
|
{
|
|
int this_cpu = raw_smp_processor_id();
|
|
|
|
if (likely(preempt_count()))
|
|
goto out;
|
|
|
|
if (irqs_disabled())
|
|
goto out;
|
|
|
|
/*
|
|
* Kernel threads bound to a single CPU can safely use
|
|
* smp_processor_id():
|
|
*/
|
|
if (current->nr_cpus_allowed == 1)
|
|
goto out;
|
|
|
|
/*
|
|
* It is valid to assume CPU-locality during early bootup:
|
|
*/
|
|
if (system_state < SYSTEM_SCHEDULING)
|
|
goto out;
|
|
|
|
/*
|
|
* Avoid recursion:
|
|
*/
|
|
preempt_disable_notrace();
|
|
|
|
if (!printk_ratelimit())
|
|
goto out_enable;
|
|
|
|
printk(KERN_ERR "BUG: using %s%s() in preemptible [%08x] code: %s/%d\n",
|
|
what1, what2, preempt_count() - 1, current->comm, current->pid);
|
|
|
|
printk("caller is %pS\n", __builtin_return_address(0));
|
|
dump_stack();
|
|
|
|
out_enable:
|
|
preempt_enable_no_resched_notrace();
|
|
out:
|
|
return this_cpu;
|
|
}
|
|
|
|
notrace unsigned int debug_smp_processor_id(void)
|
|
{
|
|
return check_preemption_disabled("smp_processor_id", "");
|
|
}
|
|
EXPORT_SYMBOL(debug_smp_processor_id);
|
|
NOKPROBE_SYMBOL(debug_smp_processor_id);
|
|
|
|
notrace void __this_cpu_preempt_check(const char *op)
|
|
{
|
|
check_preemption_disabled("__this_cpu_", op);
|
|
}
|
|
EXPORT_SYMBOL(__this_cpu_preempt_check);
|
|
NOKPROBE_SYMBOL(__this_cpu_preempt_check);
|