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Date: Mon, 23 Sep 2002 00:50:04 +0200 (CEST)
From: Ingo Molnar <mingo@elte.hu>
Reply-To: Ingo Molnar <mingo@elte.hu>
To: Karim Yaghmour <karim@opersys.com>
Cc: Linus Torvalds <torvalds@transmeta.com>,
       Roman Zippel <zippel@linux-m68k.org>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       LTT-Dev <ltt-dev@shafik.org>
Subject: Re: [PATCH] LTT for 2.5.38 1/9: Core infrastructure
In-Reply-To: <3D8E3FA9.7389A61F@opersys.com>
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a number of suggestions to make the tracer truly lightweight:

 - remove the 'event registration' and callback stuff. It just introduces
   unnecessery runtime overhead. Use an include file as a registry of
   events instead. This will simplify things greatly. Why do you need a
   table of callbacks registered to an event? Nothing in your patches
   actually uses it ... Just use one tracing function that copies the
   arguments into a per-CPU ringbuffer. It's really just a few lines.

 - do not disable interrupts when writing events. I used this method in
   a tracer and it works well. Just get an irq-safe index to the trace
   ring-buffer and fill it in. [eg. on x86 incl can be used for this
   purpose.]

 - get rid of p->trace_info and the pending_write_count - it's completely
   unnecessery.

 - drivers/trace/tracer.c is a complex mess of strange coding style and
   #ifdefs, it's not proper Linux kernel code.

it's possible to have lightweight tracing - this patch clearly is not
achieving that goal yet.

	Ingo

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