Xen devel - Jan 2009 - [PATCH 1/4] X86 microcode: cancel redundant input parameter of microcode functions

X86 microcode: cancel redundant input parameter of microcode functions

Cancel redundant input parameter ''uci'', since it can get from
another input parameter ''cpu'' as index.

Signed-off-by: Liu, Jinsong <jinsong.liu@intel.com>

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On Thursday 22 January 2009 04:08:21 Liu, Jinsong wrote:
> X86 microcode: cancel redundant input parameter of microcode functions
>
> Cancel redundant input parameter ''uci'', since it can get
from another input
> parameter ''cpu'' as index.
>
> Signed-off-by: Liu, Jinsong <jinsong.liu@intel.com>
I added the parameter ''uci'' to reduce dependency on a global
variable.
That improves reentrancy and cache locality.

If you want to go a step forward rather back, then remove the
''cpu'' parameter
instead.

Christoph

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Christoph Egger wrote:
> On Thursday 22 January 2009 04:08:21 Liu, Jinsong wrote:
>> X86 microcode: cancel redundant input parameter of microcode
>> functions 
>> 
>> Cancel redundant input parameter ''uci'', since it can
get from
>> another input parameter ''cpu'' as index. 
>> 
>> Signed-off-by: Liu, Jinsong <jinsong.liu@intel.com>
> 
> I added the parameter ''uci'' to reduce dependency on a
global variable.
> That improves reentrancy and cache locality.
> 
> If you want to go a step forward rather back, then remove the
''cpu''
> parameter instead.
> 
> Christoph
I think the input parameter ''cpu'' is better than
''uci'' since ''cpu'' is much clear to developer
with explicit meaning, so between the 2 redundant parameters
''uci'' and ''cpu'', we should remove
''uci'', just like what native linux microcode functions do.

As for cache locality, it''s not important for microcode functions since
it''s not in key path, seldom be called. BTW, we''d better keep
consistent with native linux code for the sake of futher porting and upgrade,
you know, the latest linux kernel (2.6.28) still has some issues for microcode
...

Thanks,
Jinsong
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On Thursday 22 January 2009 11:54:15 Liu, Jinsong wrote:
> Christoph Egger wrote:
> > On Thursday 22 January 2009 04:08:21 Liu, Jinsong wrote:
> >> X86 microcode: cancel redundant input parameter of microcode
> >> functions
> >>
> >> Cancel redundant input parameter ''uci'', since it
can get from
> >> another input parameter ''cpu'' as index.
> >>
> >> Signed-off-by: Liu, Jinsong <jinsong.liu@intel.com>
> >
> > I added the parameter ''uci'' to reduce dependency on
a global variable.
> > That improves reentrancy and cache locality.
> >
> > If you want to go a step forward rather back, then remove the
''cpu''
> > parameter instead.
> >
> > Christoph
>
> I think the input parameter ''cpu'' is better than
''uci'' since ''cpu'' is much
> clear to developer with explicit meaning, so between the 2 redundant
> parameters ''uci'' and ''cpu'', we should
remove ''uci'', just like what native
> linux microcode functions do.
What linux does, doesn''t matter here. Dom0 just has to make the
hypercall.
This is nothing linux specific.
> As for cache locality, it''s not important for microcode functions
since
> it''s not in key path, seldom be called.
Right, but better reentrancy is always good.
> BTW, we''d better keep consistent 
> with native linux code for the sake of futher porting and upgrade, you
> know, the latest linux kernel (2.6.28) still has some issues for microcode
> ...
You should have hear yourself.

Someone else can say:

BTW, we''d better keep consistent
with native Solaris code for the sake of further porting and upgrade. It 
doesn''t suffer on the Linux issues.

And another guy can say:

BTW, we''d better keep consistent with native BSD code for the sake
of further porting and upgrade.


You see what I mean?


Christoph


-- 
---to satisfy European Law for business letters:
Advanced Micro Devices GmbH
Karl-Hammerschmidt-Str. 34, 85609 Dornach b. Muenchen
Geschaeftsfuehrer: Jochen Polster, Thomas M. McCoy, Giuliano Meroni
Sitz: Dornach, Gemeinde Aschheim, Landkreis Muenchen
Registergericht Muenchen, HRB Nr. 43632


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On 22/01/2009 11:07, "Christoph Egger" <Christoph.Egger@amd.com>
wrote:
>> I think the input parameter ''cpu'' is better than
''uci'' since ''cpu'' is much
>> clear to developer with explicit meaning, so between the 2 redundant
>> parameters ''uci'' and ''cpu'', we
should remove ''uci'', just like what native
>> linux microcode functions do.
> 
> What linux does, doesn''t matter here. Dom0 just has to make the
hypercall.
> This is nothing linux specific.
Like much of Xen''s low-level platform code, our microcode mechanism has
direct Linux heritage. Hence keeping as close as possible to those roots
makes upgrades from kernel.org upstream much easier. Hence there is good
reason for caring about closeness to Linux code compared with
solaris/bsd/...

 -- Keir



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