linux-kernel - Re: RE: [PATCH v10 16/24] x86/resctrl: Add interface to the assign counter

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Message-ID: <8cffb2ad-6645-45a4-8d05-c967c82eb111@amd.com>
Date: Fri, 13 Dec 2024 10:54:46 -0600
From: "Moger, Babu" <bmoger@....com>
To: "Luck, Tony" <tony.luck@...el.com>, Babu Moger <babu.moger@....com>
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Subject: Re: RE: [PATCH v10 16/24] x86/resctrl: Add interface to the assign
 counter

Hi Tony,

On 12/13/2024 10:24 AM, Luck, Tony wrote:
>> It is right thing to continue assignment if one of the domain is out of
>> counters. In that case how about we save the error(say error_domain) and
>> continue. And finally return success if both ret and error_domain are zeros.
>>
>>     return ret ?  ret : error_domain:
> 
> If there are many domains, then you might have 3 succeed and 5 fail.
> 
> I think the best you can do is return success if everything succeeded
> and an error if any failed.

Yes. The above check should take care of this case.

> 
> You have the same issue if someone tries to update multiple things
> with a single write to mbm_assign_control:
> 
> # cat > mbm_assign_control << EOF
> c1/m78/0=t;1=l;
> c1/m79/0=t;1=l
> c1/m80/0=t;1=l;
> c1/m81/0=t;1=l;
> EOF
> 
> Those get processed in order, some may succeed, but once a domain
> is out of counters the rest for that domain will fail.

Yes. I see the similar type of processing for schemata.
It is processed sequentially. If one fails, it returns immediately.

ret = rdtgroup_parse_resource(resname, tok, rdtgrp);
if (ret)
       goto out;

I feel it is ok to keep same level of processing.

> 
> Updates to schemata are handled in multiple passes to either have
> all succeed or all fail. But the only problems that can occur are user
> syntax/range issues. So it's a lot simpler.
> 
> For writes to mbm_assign_control I think it's okay to document that
> some requests may have been applied even though the whole request
> reports failure. The user can always read the file to check status.

Yes. We can document this.
> 
> -Tony