2010/8/11 Attilio Rao <atti...@freebsd.org>: > 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.
And besides we have other patterns running with interrupts disabled taking care of preemption as well (I think I already pointed to one, I think you could find others easilly). 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"
