linux-kernel - Re: [PATCH 2/3] x86/intel_rdt: CBM overlap should also check for overlap with CDP peer

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Date:   Wed, 3 Oct 2018 12:51:38 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     fenghua.yu@...el.com, tony.luck@...el.com, jithu.joseph@...el.com,
        gavin.hindman@...el.com, dave.hansen@...el.com, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] x86/intel_rdt: CBM overlap should also check for
 overlap with CDP peer

Hi Thomas,

On 10/3/2018 12:43 PM, Thomas Gleixner wrote:
> On Wed, 3 Oct 2018, Reinette Chatre wrote:
>> On 10/3/2018 12:02 AM, Thomas Gleixner wrote:
>>>> +{
>>>> +	struct rdt_resource *r_cdp;
>>>> +	struct rdt_domain *d_cdp;
>>>> +	bool ret;
>>>> +
>>>> +	ret = _rdtgroup_cbm_overlaps(r, d, _cbm, closid, exclusive);
>>>> +	if (ret)
>>>> +		return ret;
>>>
>>>   	if (__rdtgroup_cbm_overlaps(r, d, _cbm, closid, exclusive))
>>> 		return true;
>>>
>>>> +
>>>> +	if (rdt_cdp_peer_get(r, d, &r_cdp, &d_cdp) == 0)
>>>> +		return _rdtgroup_cbm_overlaps(r_cdp, d_cdp, _cbm,
>>>> +					      closid, exclusive);
>>>
>>> 	if (rdt_cdp_peer_get(r, d, &r_cdp, &d_cdp) < 0)
>>> 		return false;
>>>
>>> 	return __rdtgroup_cbm_overlaps(r_cpd, d_cdp, _cbm, closid, exclusive);
>>>
>>> Makes the whole thing more obvious.
>>
>> I think a different change is needed to support the request from your
>> review of the first patch to propagate that unthinkable error where only
>> one of the CDP peers could have an rdt_domain associated with it.
>>
>> In the above that error in question from rdt_cdp_peer_get() will be lost.
>>
>> I could do the following in support of propagating that error (note that
>> in support of the code below __rdtgroup_cbm_overlaps() also changes to
>> return int instead of bool):
>>
>> int rdtgroup_cbm_overlaps(struct rdt_resource *r, struct rdt_domain *d,
>>                           u32 cbm, int closid, bool exclusive)
>> {
>>         struct rdt_resource *r_cdp;
>>         struct rdt_domain *d_cdp;
>>         int ret;
>>
>>         if (__rdtgroup_cbm_overlaps(r, d, cbm, closid, exclusive))
>>                 return 1;
>>
>>         ret = rdt_cdp_peer_get(r, d, &r_cdp, &d_cdp);
>>         if (ret == -ENOENT) {
>>                 return 0;
>>         } else if (ret == -EINVAL) {
>>                 rdt_last_cmd_puts("Error finding CDP peer\n");
>>                 return ret;
>>         } else {
>>                 return  __rdtgroup_cbm_overlaps(r_cdp, d_cdp, cbm,
>>                                                 closid, exclusive);
>>         }
>>
>>         return -EINVAL;
>> }
>>
>> With the above change in rdtgroup_cbm_overlaps() the call sites then
>> change to for example:
>>
>>         ret = rdtgroup_cbm_overlaps(r, d, cbm_val, rdtgrp->closid, true);
>>         if (ret < 0) {
>>                 /* last_cmd_status already populated with error */
>>                 return -EINVAL;
>>         } else if (ret == 1) {
>>                 rdt_last_cmd_puts("overlaps with exclusive group\n");
>>                 return -EINVAL;
>>         }
>>         /* fall through when no overlap detected */
>>
>> Would this be acceptable?
> 
> We really have to think about that whether it's worth it. Looking at the
> resulting code I doubt it. Then I'd rather prefer the warnon and the
> simpler code. But either way works for me.

Thank you very much. I'll resubmit with the changes you prefer.

Reinette