Forums

the proper size of cache line

Started by Unknown August 6, 2007
Hi,all
    Now I am developing video application on Freescale's SC3400 core.
I am surprised to find that the size of cache line of Dcache  is 256
bytes. If you access uncached memory, it will load 256 bytes into the
cache. In my opinion, the size of cache line may be too large and will
not efficient in video applications.  So I get  the manuals of DM642
and Blackfin from website, and find the size of cache line on these
two processors is 32 bytes. These three processor competes for the
same market but the  size of cache line is so different. Can I have
your opinions?

Best Regards
Jogging


joggingsong@gmail.com wrote:
> Hi,all > Now I am developing video application on Freescale's SC3400 core. > I am surprised to find that the size of cache line of Dcache is 256 > bytes. If you access uncached memory, it will load 256 bytes into the > cache.
Disclaimer: I am not familiar with SC3400 so the foregoing is my own speculations. I assume Dcache is data cache, yes? Looks like they meant to match the cache lines with SDRAM pages. This could be a little bit more efficient and simplify the controller also.
> In my opinion, the size of cache line may be too large and will > not efficient in video applications. So I get the manuals of DM642 > and Blackfin from website, and find the size of cache line on these > two processors is 32 bytes.
The cache line that big should work not like a cache with arbitrary mapping, but more like loading a chunk of data into fast memory, processing it and flushing it back.
> These three processor competes for the > same market but the size of cache line is so different. Can I have > your opinions?
It would be necessary to order the data in the memory in the proper way. Otherwise this cache with 256b lines will be very inefficient. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
On Aug 6, 11:48 pm, Vladimir Vassilevsky <antispam_bo...@hotmail.com>
wrote:
> joggings...@gmail.com wrote:
Thanks, Vladimir.
> > Hi,all > > Now I am developing video application on Freescale's SC3400 core. > > I am surprised to find that the size of cache line of Dcache is 256 > > bytes. If you access uncached memory, it will load 256 bytes into the > > cache. > > Disclaimer: I am not familiar with SC3400 so the foregoing is my own > speculations. I assume Dcache is data cache, yes? > > Looks like they meant to match the cache lines with SDRAM pages. This > could be a little bit more efficient and simplify the controller also.
I don't understand SDRAM page, do you mean one row of memory array in the SDRAM. In your opinion, when we select SDRAM chips, we should consider the page size of SDRAM?
> > > In my opinion, the size of cache line may be too large and will > > not efficient in video applications. So I get the manuals of DM642 > > and Blackfin from website, and find the size of cache line on these > > two processors is 32 bytes. > > The cache line that big should work not like a cache with arbitrary > mapping, but more like loading a chunk of data into fast memory, > processing it and flushing it back. > > > These three processor competes for the > > same market but the size of cache line is so different. Can I have > > your opinions? > > It would be necessary to order the data in the memory in the proper way. > Otherwise this cache with 256b lines will be very inefficient. > > Vladimir Vassilevsky > > DSP and Mixed Signal Design Consultant > > http://www.abvolt.com
Jogging