Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751877Ab3JAHUB (ORCPT ); Tue, 1 Oct 2013 03:20:01 -0400 Received: from ozlabs.org ([203.10.76.45]:44931 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751663Ab3JAHT6 (ORCPT ); Tue, 1 Oct 2013 03:19:58 -0400 Date: Tue, 1 Oct 2013 17:19:55 +1000 From: Michael Ellerman To: Alexander Gordeev Cc: Tejun Heo , Bjorn Helgaas , Benjamin Herrenschmidt , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "linux-pci@vger.kernel.org" , "linux-ide@vger.kernel.org" , Ingo Molnar , Joerg Roedel , Jan Beulich , linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v2 2/6] PCI/MSI: Factor out pci_get_msi_cap() interface Message-ID: <20131001071954.GG17966@concordia> References: <20130918142231.GA21650@mtj.dyndns.org> <20130918165045.GB2353@dhcp-26-207.brq.redhat.com> <20130920082458.GA10507@dhcp-26-207.brq.redhat.com> <20130920122736.GD7630@mtj.dyndns.org> <20130925180220.GB26273@google.com> <20130925205804.GA21737@dhcp-26-207.brq.redhat.com> <20130925210016.GA8926@htj.dyndns.org> <20130926074646.GA16774@dhcp-26-207.brq.redhat.com> <20130926131147.GA31249@mtj.dyndns.org> <20130926143901.GE16774@dhcp-26-207.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130926143901.GE16774@dhcp-26-207.brq.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: 1635 Lines: 31 On Thu, Sep 26, 2013 at 04:39:02PM +0200, Alexander Gordeev wrote: > On Thu, Sep 26, 2013 at 09:11:47AM -0400, Tejun Heo wrote: > > > Because otherwise we will re-introduce a problem described by Michael: > > > "We have a small number of MSIs available, limited by hardware & > > > firmware, if we don't impose a quota then the first device that probes > > > will get most/all of the MSIs and other devices miss out." > > > > Still not following. Why wouldn't just letting the drivers request > > the optimal number they want and falling back to single interrupt mode > > work? ie. why can't we just have an all or nothing interface? > > I can imagine a scenario where the first device probes in, requests its > optimal number, acquires that number and exhausts MSIs in pSeries firmware. > The next few devices possibly end up with single MSI, since no MSIs left > to satisfy their optimal numbers. If one of those single-MSI'ed devices > happened to be a high-performance HBA hitting a degraded performance that > alone would force (IBM) to introduce the quotas. Yes that's exactly the scenario, and I didn't imagine it, our test people actually hit it and yelled at me. I don't remember exactly which adapters it was, I might be able to find the details if I looked hard, a quick search through my mail archive didn't find it - it might have come in via irc / bugzilla etc. cheers -- 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/