Messages in this thread | | | Date | Mon, 23 Sep 2002 01:32:30 +0200 (CEST) | From | Ingo Molnar <> | Subject | Re: [ltt-dev] Re: [PATCH] LTT for 2.5.38 1/9: Core infrastructure |
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this is that a trace point should do, at most:
---------------------> task_t *tracer_task;
int curr_idx[NR_CPUS]; int curr_pending[NR_CPUS];
struct trace_event **trace_ring;
void trace(event, data1, data2, data3) { int cpu = smp_processor_id(); int idx, pending, *curr = curr_idx + cpu; struct trace_event *t; unsigned long flags;
if (!event_wanted(current, event, data1, data2, data3)) return;
local_irq_save(flags);
idx = ++curr_idx[cpu] & (NR_TRACE_ENTRIES - 1); pending = ++curr_pending[cpu];
t = trace_ring[cpu] + idx;
t->event = event; rdtscll(t->timestamp); t->data1 = data1; t->data2 = data2; t->data3 = data3;
if (curr_pending == TRACE_LOW_WATERMARK && tracer_task) wake_up_process(tracer_task);
local_irq_restore(flags); }
this should cover most of what's needed. The event_wanted() filter function should be made as fast as possible. Note that the irq-disabled section is not strictly needed but nice and also makes it work on the preemptible kernel. (It's not a big issue at all to run these few instructions with irqs disabled.)
[there are also other details like putting curr_index and curr_pending into the per-cpu area and similar stuff.]
Ingo
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