[XviD-devel] Re: Re: performance analysis results
Venkata Tumati
vt35 at cornell.edu
Sun Mar 9 19:56:27 CET 2003
I mean the time, when I said cycles.
On Sun, 9 Mar 2003, Venkata Tumati wrote:
> Hi,
> I was doing some performance analysis using SGI Speedshop on xvid.
> 1st setup was using xvid_20021230 and the 2nd setup was the latest
> download from yesterday xvidcore-0.9.1.
You mean the xvidcore-0.9.1 archive, available from from www.xvid.org?
Or some CVS version?
>>>>>Yes xvidcore-0.9.1 from xvid.org
> The results are pretty contrasting. Any way here is the summary. Also
> I made some changes to xvid_encraw.c and xvid_decraw.c to encode 3
> visual objects; I create three instances of the encoder and store the
> results sequentially in a file. For decoding I use the final output
> from the encoding of 3visual objects and decode it. I hope this is how
> multiple visual are encoded.
I'm pretty sure that it's not, because XVID doesn't support multiple
visual objects. You would have to change several MPEG-headers, not only
encode three time.
>>>>>What do you mean can I get more information how to encode multiple
>>>>>visual objects, I don't want to do some wrong things and get
garbage >>>>>numbers
> All the tests were run on SGI R12k 300mhz don't know the exact cache
> config but I think it has a 2MB L2 cache.
I found some CPU specs, maybe wrong, but:
L1 cache size - 32 KB for instruction cache and 32 KB for data cache
L1 cache line - 64 bytes for instruction cache and 32 bytes for data
cache
L2 cache line - 128 bytes
That's pretty weird... 32 byte cacheline for L1-cacheline on a 64bit
CPU??? But 128 for L2...
If you are interested in the truth, you can test yourself with
one of the many memory/latency benchmarks like the great
http://www.cwi.nl/~manegold/Calibrator/calibrator.shtml
Usually the peaks at L1- and L2- cache are very well visible,
also the stride values which correspond to length of cacheline.
> Xvidcore-0.9.1:(look the total time for each config)
> [...]
> Does any body know why we are having more L1 cache misses, what
> changes to the code are causing this. Is this due to some
> optimizations when the code is compiled?
This slowdown is too much to be explained by 0.5% of extra L1
cache-misses. Most likely other options have changed, too, either
compiling or encoding/decoding.
Maybe you can do a profiling run to tell which routine it was that
slowed down that much?
gruel
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