linux-kernel - Re: [PATCH 7/8] x86/intel_rdt/mba: Add schemata file support for MBA

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Date:   Tue, 17 Jan 2017 17:03:51 -0800 (PST)
From:   Shivappa Vikas <vikas.shivappa@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
cc:     Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        vikas.shivappa@...el.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 7/8] x86/intel_rdt/mba: Add schemata file support for
 MBA



On Mon, 16 Jan 2017, Thomas Gleixner wrote:

> On Tue, 10 Jan 2017, Vikas Shivappa wrote:
>> + * @display_str:		Format string to show schemata
>> + * @validate:			API to validate the ctrl values.
>>   * @info_files:		resctrl info files for the resource
>>   * @infofiles_len:		Number of info files
>>   * @max_delay:		Max throttle delay
>> @@ -99,6 +101,9 @@ struct rdt_resource {
>>  	int			cbm_len;
>>  	int			min_cbm_bits;
>>  	u32			no_ctrl;
>> +	char			*display_str;
>> +	int (*validate)		(char *buf, unsigned long *data,
>> +				  struct rdt_resource *r);
>
> Again this display and validation change wants to be seperate from the
> bandwidth stuff.
>
> It's not rocket science to split patches into preparatory and
> implementation parts.

Will split.

>
>> +	r->display_str = kstrdup("%d=%d", GFP_KERNEL);
>> +	if (!r->display_str)
>> +		return -ENOMEM;
>
> And the point of this allocation is? To consume extra memory for a constant
> string which is in const data anyway.
>
>       r->display_str = "%d=%d";

Ok will fix to const string.

>
> does not need allcotion and consumes exactly the same amount of const data
> as the above. Oh well...
>
>> -static inline bool get_rdt_resources(void)
>> +static inline int get_rdt_resources(void)
>>  {
>
> And the point of this change is? Lots of churn to return the same -ENODEV
> value at the call site. So why are you trying to return other values
> instead of the simple boolean success/fail decision?
>
>>  /*
>> + * Check whether MBE 'throttle by' value is correct.
>> + *	As per the SDM, when the scale is linear the
>> + *	throttle_by granularity is '100 - max_thrtl_by'
>> + *	and when its non-linear it is 'power of 2'.
>
> That's wrong. We really want to let the user set a bandwidth percentage
> value from 0 - 100 %. And then adjust it to the proper value which the
> hardware can provide. So the user value is independent from granularity,
> linear and the max throttling allowed.
>
>>  /*
>> - * Read one cache bit mask (hex). Check that it is valid for the current
>> - * resource type.
>> + * Read the user RDT control value into tempory buffer:
>> + * Cache bit mask (hex) or Memory b/w throttle (decimal).
>> + * Check that it is valid for the current resource type.
>>   */
>> -static int parse_cbm(char *buf, struct rdt_resource *r)
>> +static int parse_ctrls(char *buf, struct rdt_resource *r)
>>  {
>>  	unsigned long data;
>> -	int ret;
>> +	int ret = 0;
>
> What's the purpose of initializing ret to 0 if the next action is assigning
> ret the return value of the validate function?

Will fix.

Thanks,
Vikas

>
>> -	ret = kstrtoul(buf, 16, &data);
>> -	if (ret)
>> -		return ret;
>> -	if (!cbm_validate(data, r))
>> -		return -EINVAL;
>> +	ret = r->validate(buf, &data, r);
>>  	r->tmp_ctrl[r->num_tmp_ctrl++] = data;
>>
>> -	return 0;
>> +	return ret;
>>  }
>
> Thanks,
>
> 	tglx
>