Re: [Xen-devel] [PATCH v4 21/24] tools: L2 CAT: support get HW info for L2 CAT.

[Yi Sun <yi.y.sun@xxxxxxxxxxxxxxx>]

On 17-01-09 09:26:17, Wei Liu wrote:
> On Mon, Jan 09, 2017 at 01:31:35AM -0700, Jan Beulich wrote:
> > >>> On 09.01.17 at 02:19, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
> > > On 17-01-06 12:04:36, Wei Liu wrote:
> > >> On Wed, Dec 14, 2016 at 12:08:01PM +0800, Yi Sun wrote:
> > >> > This patch implements xl/xc changes to support get HW info
> > >> > for L2 CAT.
> > >> > 
> > >> > 'xl psr-hwinfo' is updated to show both L3 CAT and L2 CAT
> > >> > info.
> > >> > 
> > >> > Example(on machine which only supports L2 CAT):
> > >> > Cache Monitoring Technology (CMT):
> > >> > Enabled         : 0
> > >> > Cache Allocation Technology (CAT): L3
> > >> > libxl: error: libxl_psr.c:100:libxl__psr_cat_log_err_msg: CAT is not 
> > >> > enabled on the socket: No such file or directory
> > >> > Failed to get l3 cat info
> > >> 
> > >> What is this?
> > >> 
> > > The psr-hwinfo prints all features out by design. This test was executed 
> > > on a
> > > machine which only supports L2 CAT. So, the L3 CAT not supported info 
> > > will be
> > > printed out.
> > 
> > But there is an indication of error(s), which shouldn't be the case just
> > because of non-present hardware. The hypercall may return failure
> > in such a case of course, but this shouldn't propagate to error/failure
> > messages being printed (but at the same time you need to make sure
> > you don't hide actual errors). Perhaps there's a call missing querying
> > host capabilities (based on the result of which further info queries
> > would be issued)?
> > 
> 
> This is what I thought as well.
> 
> > Jan
> > 
I considered to add a sysctl interface to get feature mask back before.
Then, the application can print enabled feature list out in psr-hwinfo.

But current psr-hwinfo command implementation can have same effect. It
gets all features HW info back. For not enabled feature, such error info
is printed. Although it is not user friendly, it reduces one hypercall.

So, I have below two options:
1) Create a new sysctl interface to get feature mask and get HW info
   according to it.
2) Modify current psr-hwinfo codes only to show enabled feature HW info
   but not show error logs. Of course the libxl library interface still
   returns error to application.

Which one do you prefer? Thanks!

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