Re: How does __do_clear_user() works?

["Peter Teoh" <htmldeveloper@xxxxxxxxx>]

May be I shall share what I heard about might_sleep(), but have not
got the time to further analyse:

Read this (Ingo's solution):

http://kerneltrap.org/node/3440

On Fri, Aug 1, 2008 at 4:41 PM, Prasad Joshi <prasadjoshi124@xxxxxxxxx> wrote:
> Hi All,
>
> Here is the code for __do_clear_user, I am not getting how does it work. Can
> any one please explain?
>
> #define __do_clear_user(addr,size)                                      \
> do {                                                                    \
>         int __d0;                                                       \
>         might_sleep();                                                  \

First, is the need to make the kernel more interactive, or shortening
its latency in responding to external events (eg, interrupts).   To do
is quite simple, but tedious:   just go to every part of the kernel,
and insert the schedule() (or its equivalent of yielding the CPU).
But there are rules to follow when doing this, for example, u cannot
call schedule() while holding a spinlock.  (so sometimes u see patches
inserting a might_sleep() just before the spinlock statement:

http://readlist.com/lists/vger.kernel.org/linux-kernel/9/45309.html

)   So, how to do this in the fastest manner?

Ingenious solution was thought of:   insert these into might_sleep().
 So now might_sleep() will in fact attempt to switch the tasks to
another item on the waiting queue.   Latency reduced, and the kernel
become more interactive.

-- 
Regards,
Peter Teoh

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