Date: Wed, 11 Aug 2010 18:05:16 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Attilio Rao <attilio@freebsd.org> 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: <20100811150516.GM2396@deviant.kiev.zoral.com.ua> In-Reply-To: <20100811144646.GL2396@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> <AANLkTikmSTt7jLPMfFeSxyTi00KfvuWCHCL5XBZouf2m@mail.gmail.com> <20100811144646.GL2396@deviant.kiev.zoral.com.ua>
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--cEobB2knsyc5ebfU Content-Type: text/plain; charset=koi8-r Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Aug 11, 2010 at 05:46:46PM +0300, Kostik Belousov wrote: > On Wed, Aug 11, 2010 at 04:29:21PM +0200, Attilio Rao wrote: > > 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: > > >> >> =9A IPI handlers may run generally with interrupts disabled becau= se they > > >> >> =9A are served via an interrupt gate. > > >> >> > > >> >> =9A However, that doesn't explicitly prevent preemption and thread > > >> >> =9A migration thus scheduler pinning may be necessary in some han= dlers. > > >> >> =9A 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 > > > =9A =9A =9A =9Acpu =3D PCPU_GET(cpuid); > > > =9A =9A =9A =9Acpumask =3D PCPU_GET(cpumask); > >=20 > > 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. >=20 > spinlock_enter() disables preemption to handle the recursive > calls to spinlock_enter/leave, I think, to prevent switch on > leave. >=20 > I do understand the reason for your change. do _not_ understand. sorry. --cEobB2knsyc5ebfU Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (FreeBSD) iEYEARECAAYFAkxivCsACgkQC3+MBN1Mb4icRgCgxR/NthiQ+9cjbpaneO5HvWlA urcAoKBdnAcmts4h2LZd5Sjw75SC5PJj =cDZm -----END PGP SIGNATURE----- --cEobB2knsyc5ebfU--
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