Messages in this thread | | | Subject | Re: [PATCH 0/3][RFC] trace_printk() using percpu buffers | From | Peter Zijlstra <> | Date | Mon, 10 Oct 2011 13:04:57 +0200 |
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On Sat, 2011-10-08 at 13:02 -0400, Steven Rostedt wrote: > > Peter, > > You had issues with the previous version of my trace_printk() code. > I rewrote it to do the following. > > By default, it still uses the single buffer protected by a spinlock > and an atomic (for NMIs). The NMI case can cause dropped prints if > the NMI happens while a trace_printk() is processing.
Why bother keeping that?
> When trace_printk_percpu is enabled, either via the trace options or > the kernel command line, then two sets of percpu buffers are made, > one for normal and irqs (interrupts are still disabled), and the other > is for NMIs. These can be added or removed at anytime.
So why not allocate 4, one for {task, softirq, irq, NMI} resp, then all you need to do is disable preemption.
depending on tracing/options/trace_printk ?
> The last patch adds a CONFIG_TRACE_PRINTK_PERCPU that makes trace_printk() > permanently use two sets of per_cpu buffers, and these can not be > removed. This will give the least amount of overhead for trace_printk() > with the sacrifice of memory overhead. This is an option I could imagine > you would just set and forget about.
Is that one dereference really that expensive?
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