Messages in this thread Patch in this message | | | Date | Fri, 25 Jan 2013 14:20:03 -0500 | From | Rik van Riel <> | Subject | [DEBUG PATCH -v4 6/5] x86,smp: add debugging code to track spinlock delay value |
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Subject: x86,smp: add debugging code to track spinlock delay value
From: Eric Dumazet <eric.dumazet@gmail.com>
This code prints out the maximum spinlock delay value and the backtrace that pushed it that far.
On systems with serial consoles, the act of printing can cause the spinlock delay value to explode. It can still be useful as a debugging tool, but is probably too verbose to merge upstream in this form.
Not-signed-off-by: Rik van Riel <riel@redhat.com> Not-signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c index 8908dfc..f973fc9 100644 --- a/arch/x86/kernel/smp.c +++ b/arch/x86/kernel/smp.c @@ -165,6 +165,8 @@ static DEFINE_PER_CPU(struct delay_entry [1 << DELAY_HASH_SHIFT], spinlock_delay }, }; +static DEFINE_PER_CPU(u32, maxdelay); + void ticket_spin_lock_wait(arch_spinlock_t *lock, struct __raw_tickets inc) { __ticket_t head = inc.head, ticket = inc.tail; @@ -210,6 +212,12 @@ void ticket_spin_lock_wait(arch_spinlock_t *lock, struct __raw_tickets inc) } ent->hash = hash; ent->delay = delay; + + if (__this_cpu_read(maxdelay) * 4 < delay * 3) { + pr_err("cpu %d lock %p delay %d\n", smp_processor_id(), lock, delay>>DELAY_SHIFT); + __this_cpu_write(maxdelay, delay); + WARN_ON(1); + } } /*
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