On 06/04/23 15:38, Peter Zijlstra wrote: > On Wed, Apr 05, 2023 at 01:45:02PM +0100, Valentin Schneider wrote: >> >> I've been hacking on something like this (CSD deferral for NOHZ-full), >> and unfortunately this uses the CPU-local cfd_data storage thing, which >> means any further smp_call_function() from the same CPU to the same >> destination will spin on csd_lock_wait(), waiting for the target CPU to >> come out of userspace and flush the queue - and we've just spent extra >> effort into *not* disturbing it, so that'll take a while :( > > I'm not sure I buy into deferring stuff.. a NOHZ_FULL cpu might 'never' > come back. Queueing data just in case it does seems wasteful. Putting those callbacks straight into the bin would make my life much easier! Unfortunately, even if they really should, I don't believe all of the things being crammed onto NOHZ_FULL CPUs have the same definition of 'never' as we do :/
