Commit 346b46be authored by Fernando Luis Vázquez Cao's avatar Fernando Luis Vázquez Cao Committed by Ingo Molnar
Browse files

x86: Add per-cpu stat counter for APIC ICR read tries 



In the IPI delivery slow path (NMI delivery) we retry the ICR
read to check for delivery completion a limited number of times.

[ The reason for the limited retries is that some of the places
  where it is used (cpu boot, kdump, etc) IPI delivery might not
  succeed (due to a firmware bug or system crash, for example)
  and in such a case it is better to give up and resume
  execution of other code. ]

This patch adds a new entry to /proc/interrupts, RTR, which
tells user space the number of times we retried the ICR read in
the IPI delivery slow path.

This should give some insight into how well the APIC
message delivery hardware is working - if the counts are way
too large then we are hitting a (very-) slow path way too
often.

Signed-off-by: default avatarFernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Cc: Jörn Engel <joern@logfs.org>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/n/tip-vzsp20lo2xdzh5f70g0eis2s@git.kernel.org


[ extended the changelog ]
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent b95a7bd7

arch/x86/include/asm/apic.h

+3 −0
Original line number Diff line number Diff line
@@ -410,6 +410,9 @@ extern int wakeup_secondary_cpu_via_nmi(int apicid, unsigned long start_eip); 
#endif



#ifdef CONFIG_X86_LOCAL_APIC



DECLARE_PER_CPU(unsigned, icr_read_retry_count);



static inline u32 apic_read(u32 reg)

{

	return apic->read(reg);

arch/x86/kernel/apic/apic.c

+6 −0
Original line number Diff line number Diff line
@@ -79,6 +79,11 @@ DEFINE_EARLY_PER_CPU(u16, x86_bios_cpu_apicid, BAD_APICID); 
EXPORT_EARLY_PER_CPU_SYMBOL(x86_cpu_to_apicid);

EXPORT_EARLY_PER_CPU_SYMBOL(x86_bios_cpu_apicid);



/*

 * ICR read retry counter

 */

DEFINE_PER_CPU(unsigned, icr_read_retry_count);



#ifdef CONFIG_X86_32



/*
@@ -250,6 +255,7 @@ u32 native_safe_apic_wait_icr_idle(void) 
		send_status = apic_read(APIC_ICR) & APIC_ICR_BUSY;

		if (!send_status)

			break;

		percpu_inc(icr_read_retry_count);

		udelay(100);

	} while (timeout++ < 1000);

arch/x86/kernel/irq.c

+5 −0
Original line number Diff line number Diff line
@@ -74,6 +74,10 @@ int arch_show_interrupts(struct seq_file *p, int prec) 
	for_each_online_cpu(j)

		seq_printf(p, "%10u ", irq_stats(j)->apic_irq_work_irqs);

	seq_printf(p, "  IRQ work interrupts\n");

	seq_printf(p, "%*s: ", prec, "RTR");

	for_each_online_cpu(j)

		seq_printf(p, "%10u ", per_cpu(icr_read_retry_count, j));

	seq_printf(p, "  APIC ICR read retries\n");

#endif

	if (x86_platform_ipi_callback) {

		seq_printf(p, "%*s: ", prec, "PLT");
@@ -136,6 +140,7 @@ u64 arch_irq_stat_cpu(unsigned int cpu) 
	sum += irq_stats(cpu)->irq_spurious_count;

	sum += irq_stats(cpu)->apic_perf_irqs;

	sum += irq_stats(cpu)->apic_irq_work_irqs;

	sum += per_cpu(icr_read_retry_count, cpu);

#endif

	if (x86_platform_ipi_callback)

		sum += irq_stats(cpu)->x86_platform_ipis;

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