Messages in this thread | | | Subject | Re: [PATCH] Use uname not sysctl to get the kernel revision | From | Benjamin Herrenschmidt <> | Date | Sat, 15 Jul 2006 04:45:45 +1000 |
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On Thu, 2006-07-13 at 00:07 +0100, Alan Cox wrote: > 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
Except that "this cpu" doesn't really mean anything in userspace, and while I think Andi has some tricks to get some sort of CPU number to userspace (though it's really only valid during the execution of the instruction that reads it :) I haven't yet found an equivalent for powerpc (and possibly other architectures will have the same problem).
> 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
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