[Cbe-oss-dev] [RFC/PATCH] libspe2: use mapped dma registers to speed up proxy dma

[D. Herrendoerfer]

On Wed, 2007-05-23 at 17:57 +0900, Kazunori Asayama wrote:
[snip]
> 
> BTW, in this implementation, DMA proxy commands are always issued via
> direct access when SPE_MAP_PS is enabled. However, if DMA proxy
> commands are issued via direct access, we can't wait for completion of
> the DMAs via syscalls (poll/epoll). That means we can no longer wait
> for DMA completion by using libspe2 event API when SPE_MAP_PS is
> enabled. E.g., such a restriction makes it impossible to create
> applications which use event API to wait for PPE-initiated DMAs and do
> SPE-SPE communication via SNR. So I think we may have to introduce a
> new separate flag from SPE_MAP_PS to enable this optimized behavior,
> so that each application can choose preferable behavior.
> 
> --
> (ASAYAMA Kazunori
>   (asayama at sm.sony.co.jp))

Indeed, we discussed this briefly yesterday - but for another reason:
In HPC uses it might be preferable to turn of synchronization (locking)
in the libspe code, and have the application take care of this manually.
Since this approach brings a DMA throughput gain of over 100% it might
make sense to also add this option.

Regards,

D. Herrendoerfer