8ec
Subj : Re: Memory visibility and MS Interlocked instructions
To   : comp.programming.threads
From : Joe Seigh
Date : Fri Aug 26 2005 09:25 am

Alexander Terekhov wrote:
> Joe Seigh wrote:
> [...]
> 
>>Sun has #LoadLoad, #LoadStore, etc...  which gives you all the different
>>memory ordering that you would need. 
> 
> 
> Sun has a whole bunch of (compound) bidirectional fences. A subset 
> of Sun's fences can be used to implement unidirectional hoist/sink 
> stuff and also barrier(msync) intrinsic with "true == (msync & 
> msync_rel) && (msync & msync_acq)" precondition  

Whoa!  Define bidirectional and unidirectional first.

> 
>   ssb|hsb -> StoreStore           // eieio or {lw}sync
>   ssb|hlb -> StoreLoad            // sync
>   slb|hsb -> LoadStore            // {lw}sync
>   slb|hlb -> LoadLoad             // {lw}sync
>   rel|hsb -> StoreStore+LoadStore // {lw}sync
>   rel|hlb -> StoreLoad+LoadLoad   // sync
>   ssb|acq -> StoreStore+StoreLoad // sync
>   slb|acq -> LoadStore+LoadLoad   // {lw}sync

Suns mnemonics seem more intuitive than pirate mnemonics.
Unless you're trying to get ready for Talk Like a Pirate Day,
which is Sept. 19, BTW.

>   rel|acq -> Sledgehammer proper  // sync
LoadLoad+LoadStore+StoreStore+StoreLoad I assume.

> 
> on Sun's hardware, but Sun's model sucks because bidirectional 
> constraints are just way too heavy. As for cc/dd stuff, go read 
> D.3.3. It says that cchsb (in somewaht dumb incarnation) is implied 
> on Sparc hardware (for load{-modify-store} stuff) just like ddhlb, 
> ddhsb, and ddacq (ddhlb+ddhsb). But cchlb does require a fence (in 
> RMO): the same (trailing) MEMBAR #LoadLoad as ccacq (cchlb + cchsb). 
> 
> That does NOT mean that compilers can't be more effecient than 
> Sun's hardware regarding reordering constraints (I mean compiler 
> reordering).

What do compilers have to do with anything, other then you need
to address ordering issues with them also, i.e. the "membar" api
needs to address both.  For example a "LoadLoad" api would need
a hardware LoadLoad membar and LoadLoad ordering by the compiler.
> 
> regards,
> alexander.


-- 
Joe Seigh

When you get lemons, you make lemonade.
When you get hardware, you make software.

.

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