Messages in this thread | | | Date | Sat, 10 Aug 2013 08:42:58 -0700 | Subject | Re: [PATCH 10/13] x86: Move cond resched for copy_{from,to}_user into low level code 64bit | From | Linus Torvalds <> |
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On Fri, Aug 9, 2013 at 4:04 PM, Andi Kleen <andi@firstfloor.org> wrote: > From: Andi Kleen <ak@linux.intel.com> > > Move the cond_resched() check for CONFIG_PREEMPT_VOLUNTARY into > the low level copy_*_user code. This avoids some code bloat and > makes check much more efficient by avoiding unnecessary function calls.
May I suggest going one step further, and just removing the cond_resched() _entirely_, leaving just the debug test?
There really is zero reason for doing a cond_resched() for user accesses. If they take a page fault, then yes, by all means do that (and maybe we should add one to the page fault trap if we don't have it already), but without a page fault they really aren't that expensive.
We do many more expensive things without any cond_resched(), and doing that cond_resched() really doesn't make much sense *unless* there's a big expensive loop involved.
Most of this series looks fine, but I really think that we could/should just take that extra step, and say "no, user accesses don't imply that we need to check for scheduling".
Linus
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