linux-kernel - Re: [PATCH 2/7] x86/intel_rdt: Adds support for Class of service management

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Date:	Tue, 19 May 2015 10:33:55 -0700 (PDT)
From:	Vikas Shivappa <vikas.shivappa@...el.com>
To:	Borislav Petkov <bp@...en8.de>
cc:	Thomas Gleixner <tglx@...utronix.de>,
	Vikas Shivappa <vikas.shivappa@...el.com>,
	Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
	x86@...nel.org, linux-kernel@...r.kernel.org, hpa@...or.com,
	mingo@...nel.org, tj@...nel.org, peterz@...radead.org,
	Matt Fleming <matt.fleming@...el.com>,
	"Auld, Will" <will.auld@...el.com>, peter.zijlstra@...el.com,
	h.peter.anvin@...el.com,
	"Juvva, Kanaka D" <kanaka.d.juvva@...el.com>, mtosatti@...hat.com
Subject: Re: [PATCH 2/7] x86/intel_rdt: Adds support for Class of service
 management



On Mon, 18 May 2015, Borislav Petkov wrote:

> On Mon, May 18, 2015 at 08:41:53PM +0200, Thomas Gleixner wrote:
>>>>> +	}
>>>>> +
>>>>> +	set_bit(0, rdtss_info.closmap);
>>>>> +	rdt_root_group.clos = 0;
>>>>> +	ccm = &ccmap[0];
>>>>> +	bitmap_set(&ccm->cache_mask, 0, max_cbm_len);
>>>>> +	ccm->clos_refcnt = 1;
>>>>> +
>>>>>  	pr_info("Max bitmask length:%u,Max ClosIds: %u\n", max_cbm_len,
>>>>> maxid);
>>>>
>>>> We surely do not want to sprinkle these all over dmesg.
>>>
>>> This is just printed once! how is that sprinke all over?   - we have a dmsg
>>> print for Cache monitoring as well when cqm is enabled.
>>
>> Sorry, mapped that to the wrong function. Though the message itself is
>> horrible.
>>
>> 	  "Max bitmask length:32,Max ClosIds: 16"
>>
>> With some taste and formatting applied this would read:
>>
>>      	  "Max. bitmask length: 32, max. closids: 16"
>>
>> Can you spot the difference?
>
> I sure can.
>
> Also, I'd still like to ask about the usability of that message. What
> does it bring us?
>
> And if the dmesg ring buffer wraps around and it gets overwritten, what
> do we do then?
>
> So basically this message does tell us about some max bitmap length and
> so on. IOW, useless, right?
>
> Can it be read out from CPUID maybe? If so, stuff which is interested in
> it can generate it then.

Yes the max bitmask and max closid can be read from cpuid. the presence of rdt 
and l3 
cache alloc is indicated by rdt and cat_l3 in /proc/cpuinfo. So even if this 
message gets overwritten , user can see the feature enabled in kernel.

Can be modified somthing similar to "Intel cache allocation enabled" as well.

Thanks,
Vikas

>
> -- 
> Regards/Gruss,
>    Boris.
>
> ECO tip #101: Trim your mails when you reply.
> --
>
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