linux-kernel - RE: [PATCH]: Staging: hv: Allocate the vmbus irq dynamically

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Message-ID: <6E21E5352C11B742B20C142EB499E048014E4A@TK5EX14MBXC128.redmond.corp.microsoft.com>
Date:	Wed, 23 Feb 2011 19:22:45 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Greg KH <greg@...ah.com>, Thomas Gleixner <tglx@...utronix.de>
CC:	"gregkh@...e.de" <gregkh@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"virtualization@...ts.osdl.org" <virtualization@...ts.osdl.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>
Subject: RE: [PATCH]: Staging: hv: Allocate the vmbus irq dynamically



> -----Original Message-----
> From: Greg KH [mailto:greg@...ah.com]
> Sent: Wednesday, February 23, 2011 2:16 PM
> To: Thomas Gleixner
> Cc: KY Srinivasan; gregkh@...e.de; linux-kernel@...r.kernel.org;
> virtualization@...ts.osdl.org; devel@...uxdriverproject.org
> Subject: Re: [PATCH]: Staging: hv: Allocate the vmbus irq dynamically
> 
> On Mon, Feb 21, 2011 at 03:51:56PM +0100, Thomas Gleixner wrote:
> > On Mon, 21 Feb 2011, KY Srinivasan wrote:
> > > > > > There are various ways to solve that proper.
> > > > > >
> > > > > >  - You can provide the interrupt number from ACPI/PCI or whatever
> your HV
> > > > > >    provides as enumeration.
> > > > > >
> > > > > >  - Use a fixed vector like XEN does for the event channel
> > > > > >
> > > > > >  - Use dynamic allocation in the IOAPIC space like the kernel does for
> > > > > >    MSI(-X)
> > > > > >
> > > > > > Thanks,
> > > > > >
> > > > > > 	tglx
> > > > >
> > > > > I am not claiming that what I have done here is the best possible solution.
> > > > > However, I will submit to you that it is better than what we had here
> > > > > prior to this patch.  I will address this and a  whole lot of other issues
> > > > > in future patches.
> > > >
> > > > No, it's _NOT_ better in any way. You trade breaking your PV thing
> > > > against breaking random other drivers. Care to explain why you think
> > > > that's better ?
> > >
> > > The root device for the VM is bound to the PV driver on some distributions.
> > > So, if we cannot load the PV drivers, we do not have a system that boots.
> > > In general, the system performance without these PV drivers is so poor that
> > > for all practical purposes, having the PV drivers is almost a requirement
> > > for having a useable system. While the platform supports configuration of the
> VM with
> > > some emulated devices, it is not a recommended configuration (because of
> > > performance reasons) for Linux virtual machines on the Hyper-V platform.
> >
> > It does not matter whether it's recommended or not. If it results in a
> > non usable emulated device it's broken. Just imagine you grab the
> > serial interrupt, which results in not having a debug console. Not at
> > all acceptable.
> >
> > > I have spent significantly more time debating this patch than
> > > developing this patch that I still think improves the current
> > > driver. I will leave it to Greg and other powers that be to decide
> > > if this patch will be accepted. Let me know what your verdict is.
> >
> > As I said, any other clean solution (and I pointed out 3) over this
> > hack.
> 
> I agree, KY, please fix this up properly, I've dropped this patch from
> my queue now.

Ok; will do.

K. Y
> 
> thanks,
> 
> greg k-h

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