From: "H. Peter Anvin" Subject: Re: Subject: [PATCH 1/2] x86: get back 15 vectors Date: Mon, 04 Jan 2010 11:14:44 -0800 Message-ID: <4B423E24.90106@zytor.com> References: <4B347AEE.6030705@kernel.org> <20091228094707.GH24690@elte.hu> <4B398ECD.1080506@kernel.org> <4807377b1001031906s6b1ee576jc021da2642bb4147@mail.gmail.com> <4B415E73.1050801@kernel.org> <4B419113.1090204@kernel.org> <4B42362F.7040302@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Yinghai Lu , Jesse Brandeburg , Ingo Molnar , Thomas Gleixner , "linux-kernel@vger.kernel.org" , Andrew Morton , NetDEV list , Jesse Brandeburg To: "Eric W. Biederman" Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 01/04/2010 11:04 AM, Eric W. Biederman wrote: >> >> any reason that we can not use 0x40? > > Not that I now of. Reading the comment it looks like it was only > skipped so that the initial assignment of vectors would be. > > 0x31, 0x41, 0x51, 0x61, 0x71, 0x81, 0x91, 0xa1, 0xb1, 0xc1, 0xd1, 0xe1 > Instead of. > 0x30, 0x40, 0x50, 0x60, 0x70, 0x90, 0xa0, 0xb0, 0xc0, 0xc0, 0xe0 > > Which doesn't seem to be the worst notion, but at the point we are looking > for every vector we can get it does seem to be problematic. > This can presumably be worked around by tweaking the initial assignment algorithm slightly, without losing a whole vector to that. Also, if we abuse vector 0x1f as the IRQ reassignment vector, we free up a full 16 vectors per CPU -- this seems worthwhile especially since it is a decision that can be trivially undone in the future: this is all kernel internal, we're not creating any kind of API. -hpa