From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mtagate6.uk.ibm.com ([195.212.29.139]:19250 "EHLO mtagate6.uk.ibm.com") by vger.kernel.org with ESMTP id S932565AbWHHISo (ORCPT ); Tue, 8 Aug 2006 04:18:44 -0400 Subject: Re: [PATCH] x86_64: Make NR_IRQS configurable in Kconfig From: Martin Schwidefsky Reply-To: schwidefsky@de.ibm.com In-Reply-To: <200608080714.21151.ak@suse.de> References: <20060807194159.f7c741b5.akpm@osdl.org> <17624.7310.856480.704542@cargo.ozlabs.ibm.com> <200608080714.21151.ak@suse.de> Content-Type: text/plain Date: Tue, 08 Aug 2006 10:17:53 +0200 Message-Id: <1155025073.26277.18.camel@localhost> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org To: Andi Kleen Cc: Paul Mackerras , Andrew Morton , "Eric W. Biederman" , "Randy.Dunlap" , "Protasevich, Natalie" , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org List-ID: On Tue, 2006-08-08 at 07:14 +0200, Andi Kleen wrote: > > > > Drawback would be some more TLB misses. > > > > > > yup. On some (important) architectures - I'm not sure which architectures > > > do the bigpage-for-kernel trick. > > > > I looked at optimizing the per-cpu data accessors on PowerPC and only > > ever saw fractions of a percent change in overall performance, which > > says to me that we don't actually use per-cpu data all that much. So > > unless you make per-cpu data really really slow, I doubt that we'll > > see any significant performance difference. > > The main problem is that we would need a "vmalloc reserve first; allocate pages > later" interface. On x86 it would be easy by just splitting up vmalloc/vmap a bit > again. Does anybody else see problems with implementing that on any > other architecture? "vmalloc reserve first; allocate pages later" would be a really nice feature. We could use this on s390 to implement the virtual mem_map array spanning the whole 64 bit address range (with holes in it). To make it perfect a "deallocate pages; keep vmalloc reserve" should be added, then we could free parts of the mem_map array again on hot memory remove. I don't see a problem for s390. -- blue skies, Martin. Martin Schwidefsky Linux for zSeries Development & Services IBM Deutschland Entwicklung GmbH "Reality continues to ruin my life." - Calvin.