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

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

On 17-01-10 01:46:17, Jan Beulich wrote:
> >>> On 10.01.17 at 09:00, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
> > 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.
> >> 
> > 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!
> 
> Well, afaic I'd prefer any variant without new hypercall, as long as
> the bogus error messages go away without hiding any actual errors.
> 
> Jan

Ok, thank you!

Sun Yi

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