From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [PATCH 0/3][RFC] trace_printk() using percpu buffers
Date: Mon, 10 Oct 2011 13:04:57 +0200 [thread overview]
Message-ID: <1318244697.14400.18.camel@laptop> (raw)
In-Reply-To: <20111008170227.792806635@goodmis.org>
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?
next prev parent reply other threads:[~2011-10-10 10:59 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-08 17:02 [PATCH 0/3][RFC] trace_printk() using percpu buffers Steven Rostedt
2011-10-08 17:02 ` [PATCH 1/3][RFC] tracing: Do not allocate buffer for trace_marker Steven Rostedt
2011-10-08 17:02 ` [PATCH 2/3][RFC] tracing: Add optional percpu buffers for trace_printk() Steven Rostedt
2011-10-10 11:08 ` Peter Zijlstra
2011-10-10 12:37 ` Steven Rostedt
2011-10-10 13:04 ` Peter Zijlstra
2011-10-10 13:17 ` Steven Rostedt
2011-10-08 17:02 ` [PATCH 3/3][RFC] tracing: Add config to permanently have trace_printk() use percpu Steven Rostedt
2011-10-10 11:04 ` Peter Zijlstra [this message]
2011-10-10 12:31 ` [PATCH 0/3][RFC] trace_printk() using percpu buffers Steven Rostedt
2011-10-10 13:03 ` Peter Zijlstra
2011-10-10 13:06 ` Steven Rostedt
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