linux-kernel - Re: [PATCH v3 0/2] kvm: level irqfd and new eoifd

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Date:	Wed, 11 Jul 2012 12:18:15 +0200
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Alex Williamson <alex.williamson@...hat.com>,
	"mst@...hat.com" <mst@...hat.com>,
	"gleb@...hat.com" <gleb@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/2] kvm: level irqfd and new eoifd

On 2012-07-11 11:53, Avi Kivity wrote:
> On 07/03/2012 10:21 PM, Alex Williamson wrote:
>> Here's the latest iteration of adding an interface to assert and
>> de-assert level interrupts from external drivers like vfio.  These
>> apply on top of the previous argument cleanup, documentation, and
>> sanitization patches for irqfd.  It would be great to get this queued
>> in next for linux 3.6.
>>
>> I believe I've addressed all the previous comments, including fixing
>> the locking problems in eoifd.  I've run this with lockdep adding
>> and removing level irqfd/eoifd pairs without any problems.  Please
>> let me know if there are any further comments.  Thanks,
> 
> Is there any performance justification for level irqfd?  Don't all
> new/high bandwidth devices support msi, and this is just a legacy path?

I think we've been there before, but the situation hasn't improved much:

Apparently, some GPUs still prefer INTx over MSI. Some wireless chipsets
too. And then there is not easily replaceable legacy hardware like old
telephony adapters or industrial I/O cards etc. that want this.

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux


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