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Re: Ftrace for MIPS may hang on SMP system

To: wu zhangjin <wuzhangjin@gmail.com>
Subject: Re: Ftrace for MIPS may hang on SMP system
From: Steven Rostedt <rostedt@goodmis.org>
Date: Mon, 30 Aug 2010 16:51:45 -0400
Cc: David Daney <ddaney@caviumnetworks.com>, Ralf Baechle <ralf@linux-mips.org>, linux-mips <linux-mips@linux-mips.org>
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On Tue, 2010-08-24 at 14:25 +0800, wu zhangjin wrote:

> So, this patch is necessary to fix the deadlock and icache problem on
> RMI XLS and it will also improve the performance via reducing the
> unnecessary ipi interrupt on RML XLS and Cavium.

I was about to mention the performance boost of the patch even on
machines not affected by the lock up.

When you enable function tracing, it can update 22,000 locations. Doing
a cache invalidate 22,000 times in a row, is not very efficient. Only a
full cache flush is needed at the end of the update (except for the
module updates, which are done on a live system).

-- Steve



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