If you have a room, in real life, with no windows and a closed door and a light on, it doesn't get less bright if you open the door even though the light in the room can now escape. If that door is actually 2 portals that lets that escaped light illuminate an object that sits between them, how would that object not get more illuminated?
Digital Foundry Article Technical Discussion [2022]
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Yes it does. Light leaving the room is akin to having a surface that's a perfect absorber. If you paint the door of your room black, every other wall in your room will get slightly less bounce light and the room will be darker.
Yep. When I started working from home I repainted the room with my computer a much lighter colour and I can keep it even brighter by closing the doors.
Inuhanyou
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I love that devs tailor make their games to consoles fixed hardware. But it's hard to wrap my head around the concept of forcing rtgi, the most demanding setting, to be on for all other RT features to even work on PC.
Every other PC setting has fine grain control given to the user, so why wouldent that? Maybe someone wouldent mind disabling RTGI for just RT shadows or RT reflections. I am pretty sure there are other games that give the user the choice as to what RT features to turn on and off.
I have white shades covering large windows in my living room. At night with the lights on the room is definitely brighter with the shades down and reflecting light back into the room.
New brand of rubbish today. Typical. What are you even saying? The cache scrubber is a PS5 hardware feature that directly improves GPU memory bandwidth performance.
It is amazing how I am forbidden from topics when I speak but nonsense like this is applauded. Such a great place for debates.
Those are obvious jokes carried from the DF video which add levity to the topic.
These "jokes" are taken seriously enough to spread false misinformation. They are taken in the same context as "secret GPU" of Xbox 360, and it shouldn't. One is real and one is not. Unfortunately, Alex Battaglia of Digital Foundry fame has a moment where he trivializes a platform tech for unknown reasonings. I would rather DF focus on tech facts but whatever no big problem I'm not running the show. Would this forum tolerate the mocking of AMD Infinity Cache as if it does not offer relief of VRAM memory bandwidth? Same concept here as both techs have the same goals.
A spade is a spade. The "joke" from PSMan1700 is misinformation disguised as comedy. The fact is the cache scrubber HW does provide a more capable and performant GPU not unlike the objectives of the infinity cache. See it again.
I am disbarred from a topic and I never resorted to crass, jeering, sarcastic, uneducated remarks. I kept it tech fact based and my reward is banishment and deletion. Comments like above are waived as "joke". Is equity too much of a request here?
I want one with shader compilation scrubbers!
No, instead you were not civil towards other users. That's certainly not the way for any new poster to make themselves seem capable of having civil discussions.
This is a pure slander attack. If someone is responds to my facts with purposely smug foolishness, I have every right to call them out as a troublemaker and a baby who wants their results without facts to report for back up. What else do you call an adamant person who has no techs facts? It is fine I am done arguing over this I understand what this place is and who gets the protection and freedom.
That is not how any civil discussion sites operate. It's clear you have no intention of participating in a civil manner going forward.
My question is what are cache scrubbers, what do they do and where have they been used if they have been usedI guess the question I should be asking is what cache scrubbers even are and how they are used with PC gaming
I don’t know if the actual math can be done, but it comes across as an efficiency or cost saving technique. Basically there are let’s say 2 levels of memory (there is more), the cache is very small, but very fast, and memory which is very large but very slow.My question is what are cache scrubbers, what do they do and where have they been used if they have been used
Basically to make sure you are getting as much as you can out of your processors all your math is done as much as possible on cache. And when you’re done you write the results out to slow memory. But you didn’t clear the cache necessarily, so when you request the next batch of work from slow memory (which in turn populates tbe cache) the slow memory waits for the cpu to dump the entire contents of the cache before it lets the memory dump things into there. I believe this is called trashing or something. @sebbbi talks about it a lot.
The cache scrubbers act as fine grained eviction. It marks data in the cache that is no longer needed and it only evicts that which is marked. This means you don’t dump the entire cache, so you can save some cycles and overall it’s like a smoother flow. Ultimately, This saves a some cycles during this process. With a large cache some of this is nullified I suspect, its. It clear if cache is always trashed or if you can just put more into it if there is space. I suspect if not, then… yea. Cache scrubbers make sense. But it’s hard to tell how much benefit is had here.
On paper it sounds like an obvious evolution. But cpu IHV still have yet to do this? (or they have other methods around cache trashing management which isn't a cache scrubber) So the benefits may be for a very specific application and not a widespread benefit across the board. Not sure what the silicon costs are for this.
Neat innovation though, memory management is often overlooked and it plays a big part in performance.
We are talking about dumping the contents of everything and filling the whole cache. Vs. Fine grain eviction.
I think if nothing is needed in the cache then there is zero benefit. If there is something still needed in the cache then the cache will need to move up to the next higher level cache and retrieve it again.
But I do believe a larger cache will negate the need for fine grained eviction. But I could be wrong, there's no reason to endure cache trashing if you don't have to. I would agree with the general statement that having hardware based cache management is a good thing, but if no one is including it, then perhaps that may signal that it could also perform worse than what programmers can accomplish on their own.
TLDR; To maximize the performance of any processor, and especially GPUs, cache management is uber important. But when you work on very divergent workloads, your cache will be thrashed, and performance will drop heavily. Typically the way to work around this is to just code with cache thrashing in mind. But Sony has hardware to address it and make this less painful overall.
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I don't think that's actually what they do. As I understand it the scrubbers selectively wipe cache lines so that new data can be written to the GPU cache from the SSD without having to do a full cache flush. Cache flushes soak up GPU cycles as I understand it and so this is effectively a GPU performance boost when doing heavy streaming from the SSD. The level of that boost is open to question though and is likely not particularly significant.
The levity heaped upon them from DF and here is likely sourced from certain members of the community referencing them in a "secret sauce" fashion as some kind of performance game changer.
There's "real, and then there's "has a significant impact". The two are not necessarily equivalent in this case.
This is a great example of why the mocking exists. Because people draw equivalence between a genuinely transformative technology like Infinity cache which can massively increase effective GPU bandwidth, and cache scrubbers which are likely only providing a marginal boost under very specific circumstances.
Inuhanyou
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davis.anthony
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I've yet to see you speak any facts.
I want to be fair to CD33 however, we should not rule out that it may have significant impact for PS5. Elevating it to be something that it is not, I agree is incorrect, but the silicon was added nevertheless. Performance for PS5 may be dismal without it. It is already bandwidth starved as it is as it must share and have memory contention with the CPU. Being in a position where you can reduce bandwidth re-use as a result of cache flushing is likely an ideal piece of hardware in a closed system like PS5 where it draws the majority of it's performance from clock cycles. Cache misses will result in delays and PS5 will sit idle during those cycles instead of being used for something relevant, which in PS5's case, it doesn't have the width on the GPU to make up the differential that wider GPUs do.
Cache scrubbing is not an explicit api you develop for here, so it's important to recognize that it's always on and always working. Developers that rely on cache scrubbing may run into more challenges porting to PC at a later time.
Inuhanyou
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Thanks again iro 
I was about to ask if this "cache scrubbing" process was automated or something that had to be done by the developer. Cause it's pretty obvious if it needs dedicated resources to maintain it's not ever being touched for third party games. If Sony could automate the process it could really help as a background process.
It probably needs this type of thing. Series X i think is definitely not bandwidth starved with that insane amount of bandwidth. and I thought even at launch that 448 may not be enough for PS5. But developers seem to make due with what they've got
I was about to ask if this "cache scrubbing" process was automated or something that had to be done by the developer. Cause it's pretty obvious if it needs dedicated resources to maintain it's not ever being touched for third party games. If Sony could automate the process it could really help as a background process.It probably needs this type of thing. Series X i think is definitely not bandwidth starved with that insane amount of bandwidth. and I thought even at launch that 448 may not be enough for PS5. But developers seem to make due with what they've got
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