2010/8/11 Kostik Belousov <kostik...@gmail.com>: > On Wed, Aug 11, 2010 at 04:29:21PM +0200, Attilio Rao wrote: >> 2010/8/11 Kostik Belousov <kostik...@gmail.com>: >> > On Wed, Aug 11, 2010 at 01:21:46PM +0200, Attilio Rao wrote: >> >> 2010/8/11 Kostik Belousov <kostik...@gmail.com>: >> >> > On Wed, Aug 11, 2010 at 10:51:27AM +0000, Attilio Rao wrote: >> >> >> Author: attilio >> >> >> Date: Wed Aug 11 10:51:27 2010 >> >> >> New Revision: 211176 >> >> >> URL: http://svn.freebsd.org/changeset/base/211176 >> >> >> >> >> >> Log: >> >> >> IPI handlers may run generally with interrupts disabled because they >> >> >> are served via an interrupt gate. >> >> >> >> >> >> However, that doesn't explicitly prevent preemption and thread >> >> >> migration thus scheduler pinning may be necessary in some handlers. >> >> >> Fix that. >> >> > >> >> > How the preemption is supposed to happen ? Aside from the explicit >> >> > calls to mi_switch() from e.g. critical_exit(). >> >> >> >> IIRC it should be hardclock() willing to schedule the softclock(). It >> >> is the critical_exit() in the thread_unlock() that may trigger it >> >> (sorry for not digging more, it was a while back that I hacked this >> >> part, but I guess you can verify on your own). >> >> We already have other points within the kernel that take care of >> >> dealing with preemption/migration like lapic_handle_timer(), for >> >> example. >> > >> > Right, and if the interrupts are indeed disabled, I do not see how >> > the preemption may be triggered in the fragments like >> > cpu = PCPU_GET(cpuid); >> > cpumask = PCPU_GET(cpumask); >> >> I don't recall all the details and I have no time to dig now. However, >> also spinlock_enter() does disable explicitly preemption via >> critical_enter() after have disabled the interrupts. >> Let me CC jhb as he implemented spinlock_enter() and may have a clue >> about how preemption can happen with interrupts disabled. > > spinlock_enter() disables preemption to handle the recursive > calls to spinlock_enter/leave, I think, to prevent switch on > leave.
No. Please look at how spinlock_enter() is implemented in ia32/amd64 in order to see how it does handle recursion. Attilio -- Peace can only be achieved by understanding - A. Einstein _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
