Date: Wed, 11 Aug 2010 16:29:21 +0200 From: Attilio Rao <attilio@freebsd.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Jeff Roberson <jeff@freebsd.org>, John Baldwin <jhb@freebsd.org> Subject: Re: svn commit: r211176 - in head/sys: amd64/amd64 i386/i386 Message-ID: <AANLkTikmSTt7jLPMfFeSxyTi00KfvuWCHCL5XBZouf2m@mail.gmail.com> In-Reply-To: <20100811123430.GK2396@deviant.kiev.zoral.com.ua> References: <201008111051.o7BApRp4028538@svn.freebsd.org> <20100811105739.GJ2396@deviant.kiev.zoral.com.ua> <AANLkTikk3m-=5W7TVV5C-XM4AnwS1LuAi7GGEeP0B9dV@mail.gmail.com> <20100811123430.GK2396@deviant.kiev.zoral.com.ua>
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2010/8/11 Kostik Belousov <kostikbel@gmail.com>: > On Wed, Aug 11, 2010 at 01:21:46PM +0200, Attilio Rao wrote: >> 2010/8/11 Kostik Belousov <kostikbel@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: >> >> =C2=A0 IPI handlers may run generally with interrupts disabled becaus= e they >> >> =C2=A0 are served via an interrupt gate. >> >> >> >> =C2=A0 However, that doesn't explicitly prevent preemption and thread >> >> =C2=A0 migration thus scheduler pinning may be necessary in some hand= lers. >> >> =C2=A0 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 > =C2=A0 =C2=A0 =C2=A0 =C2=A0cpu =3D PCPU_GET(cpuid); > =C2=A0 =C2=A0 =C2=A0 =C2=A0cpumask =3D 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. Thanks, Attilio --=20 Peace can only be achieved by understanding - A. Einstein
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