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Date:   Wed, 3 Oct 2018 21:43:39 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Reinette Chatre <reinette.chatre@intel.com>
cc:     fenghua.yu@intel.com, tony.luck@intel.com, jithu.joseph@intel.com,
        gavin.hindman@intel.com, dave.hansen@intel.com, mingo@redhat.com,
        hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] x86/intel_rdt: CBM overlap should also check for
 overlap with CDP peer
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References: <cover.1537987801.git.reinette.chatre@intel.com> <262e12b66c238517c4766190dd493d937825f563.1537987801.git.reinette.chatre@intel.com> <alpine.DEB.2.21.1810030848580.1435@nanos.tec.linutronix.de> <6fc60e52-8f93-6135-78c0-254676c0c375@intel.com>
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Reinette,

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.

Thanks,

	tglx