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

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Message-ID: <20110223191617.GC1030@kroah.com>
Date:	Wed, 23 Feb 2011 11:16:17 -0800
From:	Greg KH <greg@...ah.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	KY Srinivasan <kys@...rosoft.com>,
	"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

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.

thanks,

greg k-h
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