Re: [PATCH 2.6.23] SysRq: print hotkey info while pressing undef key, try 2

From: Crutcher Dunnavant
Date: Wed Oct 24 2007 - 15:48:33 EST




Crutcher Dunnavant

On Oct 18, 2007, at 10:10 AM, Pavel Machek <pavel@xxxxxx> wrote:

Hi!

1) He has been told "recreate the problem, hit alt-sysreq- cokebottle,
and send me the results". He has a mission, and the only feedback he
needs is (a) that he hit cokebottle and not pepsibottle, and (b) the
resulting output.

2) He's already read the file in Documentation/ and just needs a reminder.
In this case, the fact it's only 2 or 3 lines and doesn't scroll other
stuff
out of sight is more important.

Screen scroll isn't a problem.

"SysRq : HELP : loglevel0-8 reBoot Crashdump tErm Full kIll saK showMem
Nice powerOff showPc show-all-timers(Q) unRaw Sync showTasks Unmount
shoW-blocked-tasks"

The above help information isn't very user-friendly.

Seems perfectly reasonably to me... parhaps "Full" should be replaced
with "Force-oom"...

In addition, that funtion has a big loop with another big loop
embedded which is very inefficient, it is intended to skip some hot


You're optimizing code that hopefully never gets executed, and even if
it does, you have the optimization *backwards*. If you're worried about
the efficiency, trim it down to output 3 lines - do you realize how many
instructions it takes in the VGA and fb drivers to actually *output* all
these lines? (Seriously - I had a 1.6Ghz P4 laptop, where scrolling the
screen with vga=791 actually ran so slowly that it horqued up the timer
initialization code. *That* was a fun bug to figure out..)

To remove a bad loop is just a plus fix. That loop is really
inefficient.

No, it is not a fix and no, it is not inefficient.

+static char __read_mostly sysrq_hot_key_table[36] = {
+ '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
+ 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
+ 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
+ 'u', 'v', 'w', 'x', 'y', 'z'

This has to go.
Pavel

Wow. I've not looked at this in a long time.
A. This imp of sysrq was designed to be run time registerable by modules.
B. Some keys aren't valid on some arches.
C. If you care about the lookup time for one table scan, sysrq can't help you anyway.

-- d
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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