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From: Thomas Gleixner <tglx@linutronix.de>
To: Micha Nelissen <micha@neli.hopto.org>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, "Venkatesh Pallipadi (Venki)" <venki@google.com>,
	linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
	Matthew Wilcox <matthew@wil.cx>
Subject: Re: [PATCH] Add support for multiple MSI on x86
Date: Tue, 8 Mar 2011 22:05:11 +0100 (CET)	[thread overview]
Message-ID: <alpine.LFD.2.00.1103082143460.2787@localhost6.localdomain6> (raw)
In-Reply-To: <4D714357.3010807@neli.hopto.org>

On Fri, 4 Mar 2011, Micha Nelissen wrote:
> Jesse Barnes wrote:
> > On Sun, 13 Feb 2011 21:25:21 +0100
> > Micha Nelissen <micha@neli.hopto.org> wrote:
> > 
> > > Patch is based on earlier patch from Matthew Wilcox.
> > 
> > I like this before when Matthew was working on it too
> 
> If I understood Thomas' concerns well, it sounds like this feature is
> inherently incompatible with big SMP systems. Therefore it has no chance of
> ever being accepted into mainline in whatever form?

First of all MSI is replaced by MSI-X which does not have the
shortcomings of MSI vs. the vector allocation.

Though if we can come up with a scheme which does not create nested
loops over possibly hundreds of CPUs with interrupts disabled and
global locks held, I have no objections.

One possible solution would be to reserve a block of vectors on all
cpus at boot time via a command line option for MSI block
allocations. That would simply use a bitmap protected by a mutex to
lookup a free vector space. That would avoid the whole loop issue and
work for most of the systems which need to deal with such MSI multi
vector devices. Warning: Just an idea :)

Thanks,

	tglx

  reply	other threads:[~2011-03-08 21:06 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-02-13 20:25 Micha Nelissen
2011-02-14 12:34 ` Ingo Molnar
2011-02-14 19:47   ` Micha Nelissen
2011-02-15  2:38     ` Ingo Molnar
2011-02-14 20:55 ` Thomas Gleixner
2011-03-04 18:37   ` Jesse Barnes
2011-06-17 17:12   ` Matthew Wilcox
2011-03-04 18:36 ` Jesse Barnes
2011-03-04 19:53   ` Micha Nelissen
2011-03-08 21:05     ` Thomas Gleixner [this message]
     [not found]       ` <35bd5f56-658b-48e3-a376-b07350a29cf6@email.android.com>
2011-03-08 21:16         ` Thomas Gleixner
     [not found]           ` <71ed11a4-aff7-4eb6-b037-0e097bb96444@email.android.com>
2011-03-08 22:13             ` Thomas Gleixner
2011-03-10  2:05           ` Roland Dreier
2011-03-10 15:33             ` Clemens Ladisch

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