Re: [PATCH 1/2] lib: more scalable list_sort()

[Andi Kleen <andi@firstfloor.org>]

Don Mullis <don.mullis@gmail.com> writes:
>
> Being just a dumb library routine, list_sort() has no idea what context
> it's been called in, how long a list a particular client could pass in,
> nor how expensive the client's cmp() callback might be.
>
> The cmp() callback already passes back a client-private pointer.
> Hanging off of this could be a count of calls, or timing information,
> maintained by the client.  Whenever some threshold is reached, the
> client's cmp() could do whatever good CPU-sharing citizenship required.

need_resched() does all the timing/thresholding (it checks the 
reschedule flag set by the timer interrupt). You just have to call it.
But preferable not in the inner loop, but in a outer one. It's
not hyper-expensive, but it's not free either.

The drawback is that if it's called the context always has to
allow sleeping, so it might need to be optional.

Anyways a better fix might be simply to ensure in the caller
that lists never get as long that they become a scheduling
hazard. But you indicated that ubifs would pass very long lists?
Perhaps ubifs (and other calls who might have that problem) simply
needs to be fixed.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.