Re: [Xen-devel] [PATCH v2 07/15] x86: implement set value flow for MBA

[Roger Pau Monn� <roger.pau@xxxxxxxxxx>]

On Thu, Aug 31, 2017 at 06:10:07PM +0800, Yi Sun wrote:
> On 17-08-31 10:30:37, Roger Pau Monn� wrote:
> > On Thu, Aug 31, 2017 at 05:13:08PM +0800, Yi Sun wrote:
> > > On 17-08-31 09:30:47, Roger Pau Monn� wrote:
> > > > On Thu, Aug 31, 2017 at 10:20:10AM +0800, Yi Sun wrote:
> > > > > On 17-08-30 09:31:04, Roger Pau Monn� wrote:
> > > > > > On Thu, Aug 24, 2017 at 09:14:41AM +0800, Yi Sun wrote:
> > > > > Even user inputs a value that does not fulfill HW requirement, HW can 
> > > > > handle it.
> > > > > So, we do not need return error to user. Otherwise, user needs to 
> > > > > know details
> > > > > of MBA.
> > > > > 
> > > > > But the issue here is how we get the actual value and show it to 
> > > > > user. There are
> > > > > two ways to do that:
> > > > > 1. When setting value, check and change it to valid one and save it 
> > > > > to our cache.
> > > > 
> > > > Instead of performing those checks manually, why not simply write the
> > > > value and read it back to see the one the hardware has actually
> > > > chosen (and cache it)?
> > > > 
> > > So, I guess you prefer optioin 2, right? If so, do we need check if input 
> > > value
> > > is valid? I see above comment that you prefer to return an error and 
> > > leave the
> > > decision to user.
> > 
> > Yes, I think so. Is reading the MSR in any performance critical path?
> > Or it's just used by the user-space tools?
> > 
> Just used by user-space tools.

Then doing a MSR read each time doesn't seem that bad IMHO (it's not a
critical path anyway).

Roger.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel