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Subject: Re: [PATCH] Use uname not sysctl to get the kernel revision
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: "Eric W. Biederman" <ebiederm@xmission.com>
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Date: Thu, 13 Jul 2006 00:07:44 +0100
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Ar Mer, 2006-07-12 am 16:26 -0600, ysgrifennodd Eric W. Biederman:
> If the lock is not short lived then the release is like to be a long
> ways off.  If the lock is not highly contended then you are not likely
> to hit the window when someone else as the contended lock.
> 
> How frequent are highly contended short lived locks in user space?

I'm not sure it matters.

If you want to do the job right then do this

- Stick an indicator of how much else wants to run on this CPU in the
vsyscall page or similar location

In your locks you can now do

              while(try_and_grab_lock() == FAILED) {
                       if (kernelpage->waiting > 0)
                              sys_somelockwaitthing()
              }

Furthermore the kernel can be intelligent about the waiting indicator
for power or other global scheduling reasons

[Disclaimer: There is a patent issue around this technique but its not
one that will impact GPL code as permissions are given for GPL use.]

Alan