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Effects of L3 cache on PCSX2
#1
I know that the difference between 3MB and 4MB really isn't a huge difference for most applications but for very CPU heavy programs like PCSX2 would a 1MB jump do anything?
i5 520m :: ATI 5650 (700, 900) :: Samsun 830 128GB SSD:: 8GB (2x4GB) RAM
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#2
Most likely not. The jump from 4MB to 6MB on my old Core2 system brought me not a single FPS.
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#3
(12-03-2010, 12:32 PM)rama Wrote: Most likely not. The jump from 4MB to 6MB on my old Core2 system brought me not a single FPS.

That's very interesting actually, what two processors? I'm talking solely cache size, so were they the same clock speed/ similar in other respects?
i5 520m :: ATI 5650 (700, 900) :: Samsun 830 128GB SSD:: 8GB (2x4GB) RAM
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#4
(12-03-2010, 12:32 PM)rama Wrote: Most likely not. The jump from 4MB to 6MB on my old Core2 system brought me not a single FPS.

Because it is still the same cache architecture and the same cache replacement policy. I'm not sure which cache replacement policy Intel uses, but if I have to guess, it would be something like least recently access. Basically, when cache is full, put new data in the slot that is least recently accessed.

Now, with Nehalem (Core i), the memory controller is on-chip so latency between cache and memory is greatly reduced. It's not the L3 cache that brings better performance. It's the on-chip memory controller.

That said, going from 4MB to 6MB to even 12MB in cache size won't yield that much performance gain, because the performance gain will be partially negated by the cache latency gain. Additionally, the architecture remains the same.

So, in the end, it's not the cache size that bring about performance gain, it's the overall architecture of the processor and how it utilizes the cache. Why? Because the cache is only there to give the illusion of large and fast memory, without actually having large and fast memory.

tl;dr version: No, there isn't much real world performance gain with larger cache or higher level cache. Unless the application does a lot of memory access, which (if I remember correctly) is not the case for PCSX2.
Nappa: Vegeta! What does the scouter say about his power level?
Vegeta: It's...one thousand and six.
Nappa: Wh-...really?
Vegeta: Yeah! Beat him up Nappa!
Nappa: Yay!
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#5
Good to know. Thanks.

So really with PCSX2 you want to look mostly for highest clockspeed for the fastest lower level cache access?
i5 520m :: ATI 5650 (700, 900) :: Samsun 830 128GB SSD:: 8GB (2x4GB) RAM
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#6
In my opinion the L3 cache is for multi task purpose like run some boinc project, pcsx2, web browser and various things in the same time. The cheapest solution is to close everything.

The purpose of the cache is to hide the memory latency in random access. There are 2 parts in the ram latency : access & transfer. The first one is quite big so the idea is to big transfer (position locality) to save multiple access time. Lots of time you do access the same data (temporal locality), so if you keep it in cache you save all the memory latency.

If the 2 previous hypothesis are wrong, your cache is useless (can also be slower than direct memory access sometimes). Data have a short lifetime so no need to have a 100mbytes cache to keep dead data.

A cache is not a memory, it is only a copy of some memory data with fast access. Unlike memory, the more bigger cache, the more slower are the access that why L1& L2 cache does not grow very big. It also depends a lots of the associativity (and so cache replacement policy). The L3 is probably direct mapped (no cache replacement policy in this case) and not efficient. A 2 or 4 times smaller cache with a better associativy can be more efficient.

Note1: some architecture like the PS2 uses real memory on chip instead of only cache.

Edit: for pcsx2 it is quite easy. Get others benchmark Wink Clockspeed is good but depends of the architecture. Fast memory with low latency could also help but the impact is probably not big.
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#7
In general though, CPU cache is probably the last thing you should worry about when choosing a processor.
Nappa: Vegeta! What does the scouter say about his power level?
Vegeta: It's...one thousand and six.
Nappa: Wh-...really?
Vegeta: Yeah! Beat him up Nappa!
Nappa: Yay!
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