at 12:54 AM, Peter Zijlstra <[email protected]> wrote: > On Wed, Oct 17, 2018 at 06:22:48PM -0700, Andy Lutomirski wrote: >>> On Oct 17, 2018, at 5:54 PM, Nadav Amit <[email protected]> wrote: >>> >>> It is sometimes beneficial to prevent preemption for very few >>> instructions, or prevent preemption for some instructions that precede >>> a branch (this latter case will be introduced in the next patches). >>> >>> To provide such functionality on x86-64, we use an empty REX-prefix >>> (opcode 0x40) as an indication that preemption is disabled for the >>> following instruction. >> >> Nifty! >> >> That being said, I think you have a few bugs. > >> First, you can’t just ignore a rescheduling interrupt, as you >> introduce unbounded latency when this happens — you’re effectively >> emulating preempt_enable_no_resched(), which is not a drop-in >> replacement for preempt_enable(). > >> To fix this, you may need to jump to a slow-path trampoline that calls >> schedule() at the end or consider rewinding one instruction instead. >> Or use TF, which is only a little bit terrifying... > > At which point we're very close to in-kernel rseq.
Interesting. I didn’t know about this feature. I’ll see if I can draw some ideas from there.
