Corey,
On Fri, Dec 4, 2009 at 11:16 PM, Corey Ashford
<cjash...@linux.vnet.ibm.com> wrote:
> I assume this is supposed to be
> .uname = "CORE_SELF",\
>
>> .udesc = "This core",\
>> .ucode = 0x40\
>> },\
>> { .uname = "BOTH_CORES",\
>
> and
> .uname = "CORE_BOTH",\
>
>> .udesc = "Both cores",\
>> .ucode = 0xc0\
>> }
>>
Yes.
>> In this particular case, a reasonable default would be
>>
>> L2_LD:ANY:MESI:CORE_SELF:u=1:k=0:i=0:e=0:c=0
>>
>> I think the only reasonable approach would be for the
>> tool to iterate over all the attributes and query 'default'
>> information. So here, it would return:
>>
>> M: is_dfl=0
>> E: is_dfl=0
>> S: is_dfl=0
>> I: is_dfl=0
>> MESI: is_dfl=1 value=0xf (unit mask value)
>> CORE_BOTH: is_dfl=0
>> CORE_SELF: is_dfl=1
>> u: is_dfl=1 value=1
>> k: is_dfl=0
>> i: is_dfl=0
>> e: is_dfl=0
>> c: is_dfl=0
>
> Just so I'm certain I understand what you are saying, if I specify
>
> L2_LD:MESI:M=0
>
> would that be an error (because M=0 conflicts with MESI) ?
>
I assume you mean M as in Modified, i.e,, from MESI. In this
case, you would get an error because MESI are managed as
unit masks, not modifiers. You'd get an error because there is
no modifier called M.
But going back to your example:
L2_LD:MESI:M
This would be legal because MESI bits can be combined. That would
be a stupid combination because you would end up measuring MESI.
The library would have to ensure that there is either at least one
unit mask set per group (here the group is M, E, S, I) or it would pick
the default (here MESI).
> I would assume it would be, and we'd have to come up with some way of
> detecting these sorts of errors. If it would be legal to specify one group
> and then alter it with an individual attribute, would the semantics differ
> from specifying them in the opposite order?
>
> L2_LD:M=0:MESI
>
Same explanation as above.
> In this case I'm saying, I want M=0 but MESI otherwise...
>
> Assuming this mixing groups and individual attributes is just not allowed,
> would the following be an error?
> L2_LD:M=0
>
> ... where you only specify one of the individual attributes and not the
> others... do the others default to something? They have is_dfl set to zero,
> but can they still have default values? Or do you start with the default
> group, and then allow modification of individual attributes (i.e. L2_LD:M=0
> would be sort of an implicit L2_LD:MESI:M=0)
>
> Also, there definitely needs to be error checking against specifying two
> groups:
>
> L2_LD:ANY:CORE_BOTH:CORE_SELF
>
Yes, in this unit mask group at most of mask can be set.
This gets me to the next challenge: how to expressed these constraints
on the unit masks in the table?
Today, on X86, the only constraint we know about is NCOMBO which
means you can have at most of unit mask at a time. But here we are
looking at something far more complicated with unit mask groups.
Maybe we could get by by simply implementing this in the actual
code and not in the table. This is how it's done today for MESI
and CORE_SELF/CORE_BOTH. The number of events where you
have to deal with this is fairly minimal on X86.
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