Date: Thu, 1 Apr 2004 11:23:35 -0500 From: John Baldwin <jhb@FreeBSD.org> To: Bruce Evans <bde@zeta.org.au> Cc: Dag-Erling =?iso-8859-1?q?Sm=F8rgrav?= <des@des.no> Subject: Re: CFD: XMLification of NOTES Message-ID: <200404011123.36337.jhb@FreeBSD.org> In-Reply-To: <20040401145536.A5418@gamplex.bde.org> References: <20040328094048.GA40406@phantom.cris.net> <200403311105.19088.john@baldwin.cx> <20040401145536.A5418@gamplex.bde.org>
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On Thursday 01 April 2004 12:11 am, Bruce Evans wrote: > On Wed, 31 Mar 2004, John Baldwin wrote: > > On Tuesday 30 March 2004 06:54 pm, Dag-Erling Sm=F8rgrav wrote: > > > CPU_I386 should not conflict with SMP, but a kernel build with both > > > will be very slow. > > > > No, it does conflict. There's no cmpxchg on i386 and no one has had the > > desire or time to emulate one for 386 machines. Doing so would be a > > waste in my opinion as well. > > des only claimed that it "should not". > > Emulating cmpxchg might make a kernel built with both slow, but the > current CPU_I386 only adds a tiny amount of slowness. It just doesn't > work on multi-CPU systems if multiple CPUs are actually used. > > Does it actually conflict in practice (except for the forced #error) > if the hardware is UP? jhb's APIC changes made configuring with SMP > not require APIC, so SMP kernels work on UP systems. Configuring with > I386_CPU shouldn't affect this, but it does because of the forced #error > at compile time. > > Bruce Hmm. Well, if the hardware is UP the kernel still does 'cmpxchg'=20 instructions, so you'd still have to emulate cmpxchg for the kernel. There= 's=20 another problem in that I think Peter changed the pmap to make using invltl= b=20 in place of invlpg be a compile time decision rather than a runtime decisio= n. If someone wants to write an in-kernel cmpxchg emulator then I wouldn't min= d=20 having I386_CPU just turn on the extra runtime checks for invltlb vs. invlp= g. =2D-=20 John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" =3D http://www.FreeBSD.org
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