Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932326Ab3FEU5e (ORCPT ); Wed, 5 Jun 2013 16:57:34 -0400 Received: from Chamillionaire.breakpoint.cc ([80.244.247.6]:42338 "EHLO Chamillionaire.breakpoint.cc" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932259Ab3FEU5b (ORCPT ); Wed, 5 Jun 2013 16:57:31 -0400 Date: Wed, 5 Jun 2013 22:56:38 +0200 From: Sebastian Andrzej Siewior To: Alexander Gordeev Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-pci@vger.kernel.org, Suresh Siddha , Yinghai Lu , Joerg Roedel , Jan Beulich , Ingo Molnar , Bjorn Helgaas Subject: Re: [PATCH v3 -tip x86/apic 1/2] PCI/MSI: Allocate as many multiple-MSIs as requested Message-ID: <20130605205638.GA5816@breakpoint.cc> References: <8575dc590b819892f366852fe50835efaf579f4f.1368431413.git.agordeev@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8575dc590b819892f366852fe50835efaf579f4f.1368431413.git.agordeev@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1355 Lines: 25 On Mon, May 13, 2013 at 11:05:48AM +0200, Alexander Gordeev wrote: > Note, although the existing 'msi_desc::multiple' field might seem > redundant, in fact in does not. In general case the number of MSIs a > PCI device is initialized with is not necessarily the closest power- > of-two value of the number of MSIs the device will send. Thus, in > theory it would not be always possible to derive the former from the > latter and we need to keep them both, to stress this corner case. > Besides, since 'msi_desc::multiple' is a bitfield, throwing it out > would not save us any space. The last paragraph makes me curious. The only place where 'multiple' is set is in do_setup_msi_irqs() and this uses the next power of two for it. And since a device is not enabled twice, it is not overridden. So it should be possible to compute 'multiple' out of 'nvec' but it saves cycles not do to so. I agree to keep 'multiple' but your argument does not seem to make sense. While nitpicking, 'nvec' might deserve a better comment than 'number of messages' since it holds the number of allocated interrupts. :) Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/