From owner-svn-src-head@FreeBSD.ORG Wed Aug 11 17:05:00 2010 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 67324106564A; Wed, 11 Aug 2010 17:05:00 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: from mail-qy0-f182.google.com (mail-qy0-f182.google.com [209.85.216.182]) by mx1.freebsd.org (Postfix) with ESMTP id B07EA8FC16; Wed, 11 Aug 2010 17:04:59 +0000 (UTC) Received: by qyk32 with SMTP id 32so437256qyk.13 for ; Wed, 11 Aug 2010 10:04:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:sender:received :in-reply-to:references:date:x-google-sender-auth:message-id:subject :from:to:cc:content-type:content-transfer-encoding; bh=qTkikgXEyKny62tmU5PHzbFAFq1AWeiDimnvwgpUpM0=; b=ksvWrp4JEsoXKzU8qkZmxc/yLE1R0gboJ2Vpg2g/C6EdwZdKU8R0OEUtvfJ5aIjpXW E0FCfe858z7YZ9svut7ri3Whn8UT1H5H+1XUT6Mi9ilsMkfUnFxEfOVuTcj003yzlUA2 d91k+mb6qS4piTpVkfg6MoYSEusQI/OxmsExg= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; b=QsRXbkiWlKzLenPCopYpCuICHJ273NHUQssI5L6MO4sFrQv2bsnQQOb4VNqrO1hKIv W+IMMU8Gg1pMYT3yetKf6WFkRc35JqeTaRPMtbI1cVXQv1uWiweXExH1CXck1AEWZX8B TAq8MuXvBN/VsLcOXUaidp+Kmo9wPuehIlPTE= MIME-Version: 1.0 Received: by 10.224.66.163 with SMTP id n35mr11009304qai.8.1281546298256; Wed, 11 Aug 2010 10:04:58 -0700 (PDT) Sender: asmrookie@gmail.com Received: by 10.229.251.6 with HTTP; Wed, 11 Aug 2010 10:04:58 -0700 (PDT) In-Reply-To: <20100811144646.GL2396@deviant.kiev.zoral.com.ua> References: <201008111051.o7BApRp4028538@svn.freebsd.org> <20100811105739.GJ2396@deviant.kiev.zoral.com.ua> <20100811123430.GK2396@deviant.kiev.zoral.com.ua> <20100811144646.GL2396@deviant.kiev.zoral.com.ua> Date: Wed, 11 Aug 2010 19:04:58 +0200 X-Google-Sender-Auth: oLzgYb2084RBRyOX2k7fi-8JCMw Message-ID: From: Attilio Rao To: Kostik Belousov Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Jeff Roberson , John Baldwin Subject: Re: svn commit: r211176 - in head/sys: amd64/amd64 i386/i386 X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 11 Aug 2010 17:05:00 -0000 2010/8/11 Kostik Belousov : > On Wed, Aug 11, 2010 at 04:29:21PM +0200, Attilio Rao wrote: >> 2010/8/11 Kostik Belousov : >> > On Wed, Aug 11, 2010 at 01:21:46PM +0200, Attilio Rao wrote: >> >> 2010/8/11 Kostik Belousov : >> >> > 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 bec= ause they >> >> >> =C2=A0 are served via an interrupt gate. >> >> >> >> >> >> =C2=A0 However, that doesn't explicitly prevent preemption and thr= ead >> >> >> =C2=A0 migration thus scheduler pinning may be necessary in some h= andlers. >> >> >> =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. > > 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 --=20 Peace can only be achieved by understanding - A. Einstein