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Knowing how long we spend in firmware calls is an important part of minimising OS jitter. This patch adds tracepoints to each OPAL call. If tracepoints are enabled we branch out to a common routine that calls an entry and exit tracepoint. This allows us to write tools that monitor the frequency and duration of OPAL calls, eg: name count total(ms) min(ms) max(ms) avg(ms) period(ms) OPAL_HANDLE_INTERRUPT 5 0.199 0.037 0.042 0.040 12547.545 OPAL_POLL_EVENTS 204 2.590 0.012 0.036 0.013 2264.899 OPAL_PCI_MSI_EOI 2830 3.066 0.001 0.005 0.001 81.166 We use jump labels if configured, which means we only add a single nop instruction to every OPAL call when the tracepoints are disabled. Signed-off-by: Anton Blanchard <anton@samba.org> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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Anton Blanchard
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Benjamin Herrenschmidt
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Jul 11, 2014
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,84 @@ | ||
| #include <linux/percpu.h> | ||
| #include <linux/jump_label.h> | ||
| #include <asm/trace.h> | ||
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| #ifdef CONFIG_JUMP_LABEL | ||
| struct static_key opal_tracepoint_key = STATIC_KEY_INIT; | ||
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| void opal_tracepoint_regfunc(void) | ||
| { | ||
| static_key_slow_inc(&opal_tracepoint_key); | ||
| } | ||
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| void opal_tracepoint_unregfunc(void) | ||
| { | ||
| static_key_slow_dec(&opal_tracepoint_key); | ||
| } | ||
| #else | ||
| /* | ||
| * We optimise OPAL calls by placing opal_tracepoint_refcount | ||
| * directly in the TOC so we can check if the opal tracepoints are | ||
| * enabled via a single load. | ||
| */ | ||
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| /* NB: reg/unreg are called while guarded with the tracepoints_mutex */ | ||
| extern long opal_tracepoint_refcount; | ||
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| void opal_tracepoint_regfunc(void) | ||
| { | ||
| opal_tracepoint_refcount++; | ||
| } | ||
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| void opal_tracepoint_unregfunc(void) | ||
| { | ||
| opal_tracepoint_refcount--; | ||
| } | ||
| #endif | ||
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| /* | ||
| * Since the tracing code might execute OPAL calls we need to guard against | ||
| * recursion. | ||
| */ | ||
| static DEFINE_PER_CPU(unsigned int, opal_trace_depth); | ||
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| void __trace_opal_entry(unsigned long opcode, unsigned long *args) | ||
| { | ||
| unsigned long flags; | ||
| unsigned int *depth; | ||
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| local_irq_save(flags); | ||
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| depth = &__get_cpu_var(opal_trace_depth); | ||
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| if (*depth) | ||
| goto out; | ||
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| (*depth)++; | ||
| preempt_disable(); | ||
| trace_opal_entry(opcode, args); | ||
| (*depth)--; | ||
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| out: | ||
| local_irq_restore(flags); | ||
| } | ||
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| void __trace_opal_exit(long opcode, unsigned long retval) | ||
| { | ||
| unsigned long flags; | ||
| unsigned int *depth; | ||
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| local_irq_save(flags); | ||
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| depth = &__get_cpu_var(opal_trace_depth); | ||
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| if (*depth) | ||
| goto out; | ||
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| (*depth)++; | ||
| trace_opal_exit(opcode, retval); | ||
| preempt_enable(); | ||
| (*depth)--; | ||
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| out: | ||
| local_irq_restore(flags); | ||
| } |
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