Date: Wed, 11 Aug 2010 19:47:09 +0200 From: Attilio Rao <attilio@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r211176 - in head/sys: amd64/amd64 i386/i386 Message-ID: <AANLkTinK33-f2rSfTj32fJrS6ftt-CQktxjbMGuu2a9n@mail.gmail.com> In-Reply-To: <4C62E112.5090206@FreeBSD.org> References: <201008111051.o7BApRp4028538@svn.freebsd.org> <4C62DADF.1000202@FreeBSD.org> <AANLkTimczmkAkqTnCDmHh1otsX1OuVggeEA8NkpY3bYO@mail.gmail.com> <4C62E112.5090206@FreeBSD.org>
next in thread | previous in thread | raw e-mail | index | archive | help
2010/8/11 John Baldwin <jhb@freebsd.org>: > Attilio Rao wrote: >> >> 2010/8/11 John Baldwin <jhb@freebsd.org>: >>> >>> 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=A0IPI handlers may run generally with interrupts disabled because = they >>>> =C2=A0are served via an interrupt gate. >>>> =C2=A0 However, that doesn't explicitly prevent preemption and thread >>>> =C2=A0migration thus scheduler pinning may be necessary in some handle= rs. >>>> =C2=A0Fix that. >>>> =C2=A0 Tested by: =C2=A0gianni >>>> =C2=A0MFC after: =C2=A0 =C2=A01 month >>> >>> Actually that does prevent preemption if you do not call any code that >>> would >>> schedule a thread. =C2=A0I think this change is all safe to revert. >> >> Do you recall, then, why lapic_handle_timer() does critical section? >> It seems to be catered by interrupt gate as well, and I don't see any >> point re-enabling them explicitly. > > Because hardclock() explicitly calls sched_add() via swi_sched() when > scheduling the softclock swi. =C2=A0The critical section there is just to= ensure > that the preemption to softclock happens after all of the clock interrupt > handlers have finished. =C2=A0However, PCPU_GET() does not call sched_add= (), so > it does not need to be protected. Oh, sorry, was looking at the -CURRENT code which had no explicit call to hardclock (it uses the new timer infrastructure, so that was not so obvious). I understand now, so I will rever the change asap. Thanks, Attilio --=20 Peace can only be achieved by understanding - A. Einstein
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?AANLkTinK33-f2rSfTj32fJrS6ftt-CQktxjbMGuu2a9n>