On Thu, Jan 14, 2021 at 01:36:27AM +0000, myfreeweb wrote: > > > On January 13, 2021 8:58:58 PM UTC, John Baldwin <j...@freebsd.org> wrote: > >It doesn't store at all because threads aren't allowed to sleep in a critical > >section, so the thread will never give up the CPU while in the FPU section. > >If > >threads can voluntarily sleep (cv_wait*, *sleep(), etc.) while using > >kernel_fpu_begin(), then NOCTX won't work and we will need something else. > > Hmm but with no storage at all, how would it work from a syscall? > The manpage does mention a "usermode save area" – I was talking about that. There is a storage for the user state, always. When NOCTX is used, FPU state is spilled into the _current_ save area, and then kernel lives to the promise that the new state after fpu_enter(NOCTX) does not ever need to be saved.
> > Linux kernel_fpu_begin starts with preempt_disable, so definitely no condvars > and the like. No idea about simple time sleeps. But amdgpu doesn't seem to do > even that. You should get enough assertions fired if something tries to context switch while entered NOCTX region. _______________________________________________ dev-commits-src-main@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/dev-commits-src-main To unsubscribe, send any mail to "dev-commits-src-main-unsubscr...@freebsd.org"
