From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Michael Neuling To: michael@ellerman.id.au Subject: Re: [RFC/PATCH] powerpc: Dynamically allocate pacas In-reply-to: <1264561612.14310.15.camel@concordia> References: <39fb8f1aeab9940b86c940b9a5f8e6bd41ec316c.1263368253.git.michael@ellerman.id.au> <31712.1264130388@neuling.org> <1264561612.14310.15.camel@concordia> Date: Wed, 27 Jan 2010 13:40:44 +1030 Message-ID: <16692.1264561844@neuling.org> Cc: linuxppc-dev@ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , > On Fri, 2010-01-22 at 16:19 +1300, Michael Neuling wrote: > >=20 > > In message <39fb8f1aeab9940b86c940b9a5f8e6bd41ec316c.1263368253.git.micha= > el@ell > > erman.id.au> you wrote: > > > On 64-bit kernels we currently have a 512 byte struct paca_struct for > > > each cpu (usually just called "the paca"). Currently they are staticall= > y > > > allocated, which means a kernel built for a large number of cpus will > > > waste a lot of space if it's booted on a machine with few cpus. > > >=20 > > > We can avoid that by only allocating the number of pacas we need at > > > boot. However this is complicated by the fact that we need to access > > > the paca before we know how many cpus there are in the system. > > >=20 > > > The solution is to dynamically allocate enough space for NR_CPUS pacas, > > > but then later in boot when we know how many cpus we have, we free any > > > unused pacas. > > >=20 > > > Lightly booted on Legacy iSeries & pSeries LPAR. > >=20 > > This is broken on 32bit CPUs. Dies at compile time with > > mpc86xx_defconfig. No paca on 32bit :-( > > Bah, who really uses 32-bit anyway .. Hehe, that's coming from the guy who tested it on iSeries... :-P Mikey