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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
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/*
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* lib/smp_processor_id.c
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*
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* DEBUG_PREEMPT variant of smp_processor_id().
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*/
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#include <linux/export.h>
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#include <linux/kprobes.h>
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#include <linux/sched.h>
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notrace static nokprobe_inline
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unsigned int check_preemption_disabled(const char *what1, const char *what2)
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{
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int this_cpu = raw_smp_processor_id();
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if (likely(preempt_count()))
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goto out;
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if (irqs_disabled())
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goto out;
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/*
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* Kernel threads bound to a single CPU can safely use
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* smp_processor_id():
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*/
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if (current->nr_cpus_allowed == 1)
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goto out;
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/*
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* It is valid to assume CPU-locality during early bootup:
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*/
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if (system_state < SYSTEM_SCHEDULING)
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goto out;
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/*
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* Avoid recursion:
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*/
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preempt_disable_notrace();
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if (!printk_ratelimit())
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goto out_enable;
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printk(KERN_ERR "BUG: using %s%s() in preemptible [%08x] code: %s/%d\n",
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what1, what2, preempt_count() - 1, current->comm, current->pid);
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printk("caller is %pS\n", __builtin_return_address(0));
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dump_stack();
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out_enable:
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preempt_enable_no_resched_notrace();
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out:
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return this_cpu;
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}
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notrace unsigned int debug_smp_processor_id(void)
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{
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return check_preemption_disabled("smp_processor_id", "");
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}
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EXPORT_SYMBOL(debug_smp_processor_id);
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NOKPROBE_SYMBOL(debug_smp_processor_id);
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notrace void __this_cpu_preempt_check(const char *op)
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{
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check_preemption_disabled("__this_cpu_", op);
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}
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EXPORT_SYMBOL(__this_cpu_preempt_check);
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NOKPROBE_SYMBOL(__this_cpu_preempt_check);
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