linux-kernel - Re: [PATCH 6/8] x86/intel_rdt/mba: Add info directory files for MBA

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Date:   Wed, 18 Jan 2017 10:08:20 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Shivappa Vikas <vikas.shivappa@...el.com>
cc:     Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
        mingo@...nel.org, peterz@...radead.org, ravi.v.shankar@...el.com,
        tony.luck@...el.com, fenghua.yu@...el.com, h.peter.anvin@...el.com
Subject: Re: [PATCH 6/8] x86/intel_rdt/mba: Add info directory files for
 MBA

On Tue, 17 Jan 2017, Shivappa Vikas wrote:
> On Mon, 16 Jan 2017, Thomas Gleixner wrote:
> 
> > On Tue, 10 Jan 2017, Vikas Shivappa wrote:
> > 
> > > Add the files in info directory for MBA.
> > > The files in the info directory are as follows :
> > >  - num_closids: max number of closids for MBA which represents the max
> > >  class of service user can configure.
> > >  - max_thrtl_by: the max throttle by values.
> > > 
> > > Throttle by can have a linear scale and non linear scale.  In linear
> > > scale, if a throttle_by value is 40%, it means that the memory b/w is
> > > throttled 'by' 40% or in other words a max of 60% b/w is allowed to
> > > pass. In non-linear scale, the throttle_by values are in 2^n
> > > granularity. The h/w does not guarantee a curve of actual throttle w.r.t
> > > the configured values. But if a throttle_by value of x > y, then x is
> > > guaranteed to throttle more b/w than y.
> > 
> > This is ambigous because that is only correct when the effective values are
> > different. x=11 and y=12 with a granularity of 10 are resulting in the same
> > throttling.
> 
> The x and y are actual values written which i will spell out. The assumption
> is that only correct values are input though because we filterout the values
> which dont follow granularity, meaning return -EINVAL when someone tries to
> write 11 when granularity is 10. This was with the idea thats its easier for
> the user to understand whats actually written. Woudl that be reasonable or
> does it need a change ?
> (Although the h/w does like you say , we can do a msr write for 11 etc ..)


> > > +/* rdtgroup information files for MBE. */
> > > +static struct rftype res_mbe_info_files[] = {
> > > +	{
> > > +		.name		= "num_closids",
> > > +		.mode		= 0444,
> > > +		.kf_ops		= &rdtgroup_kf_single_ops,
> > > +		.seq_show	= rdt_num_closids_show,
> > > +	},
> > > +	{
> > > +		.name		= "max_thrtl_by",
> > 
> > You surely could not come up with a more cryptic file name, right? What's
> > so wrong with spelling out throttle? And the whole '_by' postfix here and
> > on the other files is pointless as well.
> 
> This is due to the issue i mention in reply to 1/8.. Can be changed to

Err no. max_thrtl_by has nothing to do with 1/8. Of course you want to
expose the hardware information.

What's wrong with spelling out throttle and remove the '_by':

       max_throttle

That is readable, understandable and matches the documentation in the SDM.

It's not that hard.

Thanks,

	tglx