Re: [Xen-devel] [PATCH 1/6] x86: detect and initialize Intel CAT feature

[Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>]

On Tue, Mar 17, 2015 at 09:00:27AM -0400, Konrad Rzeszutek Wilk wrote:
> On Tue, Mar 17, 2015 at 04:11:33PM +0800, Chao Peng wrote:
> > On Fri, Mar 13, 2015 at 09:40:13AM -0400, Konrad Rzeszutek Wilk wrote:
> > > On Fri, Mar 13, 2015 at 06:13:20PM +0800, Chao Peng wrote:
> > > > Detect Intel Cache Allocation Technology(CAT) feature and store the
> > > > cpuid information for later use. Currently only L3 cache allocation is
> > > > supported. The L3 CAT features may vary among sockets so per-socket
> > > > feature information is stored. The initialization can happen either at
> > > > boot time or when CPU(s) is hot plugged after booting.
> > > > 
> > > > Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> > > > ---
> > > >  docs/misc/xen-command-line.markdown |  15 +++-
> > > >  xen/arch/x86/psr.c                  | 151 
> > > > +++++++++++++++++++++++++++++++++---
> > > >  xen/include/asm-x86/cpufeature.h    |   1 +
> > > >  3 files changed, 155 insertions(+), 12 deletions(-)
> > > > 
> > > > +    cat_cpu_init(smp_processor_id());
> > > 
> > > Do 'if (!cat_cpu_init(..)).`'
> > > 
> > > as the CPU might not support this.
> > > 
> > > At which point you should also free the cat_socket_info and
> > > not register the cpu notifier.
> > 
> > Even the booting CPU does not support this, other CPUs may still support
> > this. Generally the feature is a per-socket feature. So break here is
> > not the intention.
> 
> Oooh, and you did mention that in the git commit description and I dived
> right in the code - without looking there - sorry for that noise!
> 
> Thought I am curious - what if all the sockets don't support and the
> user does try enable it on the command line (user error)? Shouldn't we
> then figure out that all of the CPUs don't support and xfree
> cat_socket_info and not register the CPU notifier?

Ideally, we should. Tricky thing is to support cpu hot plug, which
happens not at but after the booting time.

Chao
> > 
> > Except this, all other comments will be addressed by the next version.
> 
> thank you!
> > Thanks for your time.
> > 
> > Chao
> > > 
> > > > +    register_cpu_notifier(&cpu_nfb);
> > > > +}
> > > > +
> 
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