hi :-)

2011/2/16 Mulyadi Santosa [off-list ref]:

Hi :)

On Wed, Feb 16, 2011 at 12:59, Rajat Jain [off-list ref] wrote:

quoted

Hello loody,

quoted

1. in kernel/trace, I always see "__read_mostly" at the end of
parameter is that a compiler optimization parameter?

Yes, it is a hint to the compiler that the parameter is mostly read, thus if the compiler has to make a decision between optimizing one of the read / write paths, it will optimize the read path even at the expense of write path.

To be precise, they will be grouped into same cache line as much as
possible. By doing so, those cache line won't be invalidated so often
(keeping them "hot" :) hehehhe )

I cannot find it on the gcc manual.
is it a option in kernel for kernel usage?
if so, where I can found them.
If not, can I use it on normal user level program?

BTW, i have some more questions (since it is also related to kernel, I
append in the same mail)
1. the parameters we pass to ftrace_trace_function are (unsigned long
ip, unsigned long parent_ip), which are previous and pre-previous
return address.
what can we do on these 2 addresses?

2. per kernel document, HAVE_FUNCTION_TRACE_MCOUNT_TEST is used for "
an optional optimization for the normal case" and there is a pseudo
sample code such as
+       if (function_trace_stop)
+               return;
so the optimization the config did is judge whether
"function_trace_stop" before operation, right?
Meanwhile, I found this judgement seems enable in
ftrace_test_stop_func and it is located at #ifndef
CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST.
The source code seems quite conflict with the document.


-- 
Appreciate your kind help,
miloody