Re: [Xen-devel] [PATCH for-4.12] x86/vpmu: Improve documentation and parsing for vpmu=

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 04/02/2019 14:44, Jan Beulich wrote:
>>>> On 04.02.19 at 15:22, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 04/02/2019 13:53, Jan Beulich wrote:
>>>>>> On 04.02.19 at 12:41, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>> @@ -64,37 +54,37 @@ static DEFINE_PER_CPU(struct vcpu *, last_vcpu);
>>>>  static int __init parse_vpmu_params(const char *s)
>>>>  {
>>>>      const char *ss;
>>>> +    int rc = 0, val;
>>>> +
>>>> +    do {
>>>> +        ss = strchr(s, ',');
>>>> +        if ( !ss )
>>>> +            ss = strchr(s, '\0');
>>>> +
>>>> +        if ( (val = parse_bool(s, ss)) >= 0 )
>>>> +            opt_vpmu_enabled = val;
>>>> +        else if ( !cmdline_strcmp(s, "bts") )
>>>> +            vpmu_features |= XENPMU_FEATURE_INTEL_BTS;
>>>> +        else if ( !cmdline_strcmp(s, "ipc") )
>>>> +            vpmu_features |= XENPMU_FEATURE_IPC_ONLY;
>>>> +        else if ( !cmdline_strcmp(s, "arch") )
>>>> +            vpmu_features |= XENPMU_FEATURE_ARCH_ONLY;
>>>> +        else
>>>> +            rc = -EINVAL;
>>>>  
>>>> -    switch ( parse_bool(s, NULL) )
>>>> -    {
>>>> -    case 0:
>>>> -        break;
>>>> -    default:
>>>> -        do {
>>>> -            ss = strchr(s, ',');
>>>> -            if ( !ss )
>>>> -                ss = strchr(s, '\0');
>>>> -
>>>> -            if ( !cmdline_strcmp(s, "bts") )
>>>> -                vpmu_features |= XENPMU_FEATURE_INTEL_BTS;
>>>> -            else if ( !cmdline_strcmp(s, "ipc") )
>>>> -                vpmu_features |= XENPMU_FEATURE_IPC_ONLY;
>>>> -            else if ( !cmdline_strcmp(s, "arch") )
>>>> -                vpmu_features |= XENPMU_FEATURE_ARCH_ONLY;
>>>> -            else
>>>> -                return -EINVAL;
>>>> +        s = ss + 1;
>>>> +    } while ( *ss );
>>>> +
>>>> +    /* Selecting bts/ipc/arch forces vpmu to enabled. */
>>>> +    if ( vpmu_features )
>>>> +        opt_vpmu_enabled = true;
>>> If you want to retain original behavior, the condition here would need
>>> to be "!rc && vpmu_features". It's not clear whether your modification
>>> in this regard is intentional.
>> Oh - that wasn't intentional.
>>
>> An alternative, now I think about it, is to just have the <bool>=false
>> case clear vpmu_features.  This is new behaviour, but it is more
>> consistent with how other options work, and it wasn't expressable before.
> Generally - yes. But what would e.g. "vpmu=off,ipc" end up doing in
> your new model?

The use of vpmu_features is somewhat weird.  "bts" acts as an extra
feature on top of "generally on", whereas "ipc" and "arch" act as
restrictions on top of "generally on".

I'd expect "vpmu=off,ipc" to imply "vpmu=off,ipc,on", and result in
opt_vpmu_enabled=1 and vpmu_features=ipc.

~Andrew

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