Subject: Re: [PATCH/RFC 1/2] jump label: make enable/disable o(1)
From: Peter Zijlstra <peterz@infradead.org>
To: Jason Baron <jbaron@redhat.com>
Cc: hpa@zytor.com, rostedt@goodmis.org, mingo@elte.hu,
        mathieu.desnoyers@polymtl.ca, tglx@linutronix.de, andi@firstfloor.org,
        roland@redhat.com, rth@redhat.com, masami.hiramatsu.pt@hitachi.com,
        fweisbec@gmail.com, avi@redhat.com, davem@davemloft.net,
        sam@ravnborg.org, ddaney@caviumnetworks.com, michael@ellerman.id.au,
        linux-kernel@vger.kernel.org
In-Reply-To: <20101216192303.GB2856@redhat.com>
References: <cover.1292522251.git.jbaron@redhat.com>
	 <a35b9310aafa31a9e97f5c9bad9b09e0b6cbbf79.1292522252.git.jbaron@redhat.com>
	 <1292526602.2708.57.camel@laptop>  <20101216192303.GB2856@redhat.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8BIT
Date: Thu, 16 Dec 2010 20:33:51 +0100
Message-ID: <1292528031.2708.77.camel@laptop>
Mime-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 942
Lines: 19

On Thu, 2010-12-16 at 14:23 -0500, Jason Baron wrote:
> 
> For the jump label disabled case, perf is using atomic_inc/dec and atomic_read
> to check if enabled. While other consumers (tracepoints) are just using an
> 'int'. I didn't want hurt the jump label disabled case for tracepoints.
> If we can agree to use atomic ops for tracepoints, or drop atomics from
> perf, that would simplify things. 

I had a quick look at the tracepoint stuff but got lost, but surely it
has a reference count somewhere as well, it needs to know when the last
probe goes away.. or does it check if the list is empty?

Anyway, tracepoint enable/disable isn't a real fast-path, surely it
could suffer an atomic op?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/