netdev - RE: Expose ltr/obff interface by sysfs

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Message-ID: <403610A45A2B5242BD291EDAE8B37D300FD0D988@SHSMSX102.ccr.corp.intel.com>
Date:	Wed, 11 Apr 2012 03:02:01 +0000
From:	"Hao, Xudong" <xudong.hao@...el.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: RE: Expose ltr/obff interface by sysfs

> But a better question is - why should this be done - especially from the guest
> which has a limited view of the machine? The machine might be running a lot of
> other requests so the OBFF inside the guest could be invalid.
>
Maybe I did not describe it clearly, the original idea is host admin can control the inode interface but not guest.

> -----Original Message-----
> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@...cle.com]
> Sent: Saturday, April 07, 2012 2:40 AM
> To: Hao, Xudong
> Cc: linux-pci@...r.kernel.org; netdev@...r.kernel.org;
> e1000-devel@...ts.sourceforge.net; Jesse Barnes
> Subject: Re: Expose ltr/obff interface by sysfs
> 
> On Fri, Apr 06, 2012 at 02:43:59AM +0000, Hao, Xudong wrote:
> > Hi,
> >
> > I'm working on virtualization Xen/KVM. I saw there are ltr/obff
> enabling/disabling function in pci.c, but no called till now. I want to know if
> anybody(driver developer) are working for using it? Can driver change the LTR
> latency value dynamically?
> >
> > /*
> > LTR(Latency tolerance reporting) allows devices to send messages to the root
> complex indicating their latency tolerance for snooped & unsnooped memory
> transactions.
> > OBFF (optimized buffer flush/fill), where supported, can help improve energy
> efficiency by giving devices information about when interrupts and other
> activity will have a reduced power impact.
> > */
> >
> > One way to control ltr/obff is used by driver, however, I'm considering that in
> virtualization, how guest OS driver control them. I have an idea that expose an
> inode interface by sysfs, like "reset" inode implemented in pci-sysfs.c, so that
> system user/administrator can enable/disable ltr/obff or set latency value on
> userspace, but not limited on driver. Comments?
> 
> So right now the driver inside the guest can probably see it, but can't change
> them.
> (As those requests end up being filtered).
> 
> But there is nothing wrong with your changing those values from within the
> host.
> 
> But a better question is - why should this be done - especially from the guest
> which has a limited view of the machine? The machine might be running a lot of
> other requests so the OBFF inside the guest could be invalid.
> 
> 
> >
> > < pls CC me when reply this mail, thanks >
> >
> > Best Regards,
> > Xudong Hao
> >
> > --
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