Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes: > On Wed, Oct 25, 2023 at 05:42:19AM -0400, Steven Rostedt wrote: > >> So, bit 1 is for user space to tell the kernel "please extend me", and bit >> two is for the kernel to tell user space "OK, I extended you, but call >> sched_yield() when done". > > So what if it doesn't ? Can we kill it for not playing nice ? > > [ aside from it being bit 0 and bit 1 as you yourself point out, it is > also jarring you use a numeral for one and write out the other. ] > > That said, I properly hate all these things, extending a slice doesn't > reliably work and we're always left with people demanding an ever longer > extension. > > The *much* better heuristic is what the kernel uses, don't spin if the > lock holder isn't running. Something like vcpu_is_preempted()? That helps deal with preemption once it has happened, but an ahead of time signal would be much more efficient. And, guest lock holder preemption was a big enough issue that we drop down to test-and-set spinlocks in some cases. Thanks -- ankur
