PlayStation 4 (codename Orbis) technical hardware investigation (news and rumours)

[Shifty Geezer]

No HDD would have trouble with that. However, almost all recorded material won't be saved, and every write to HDD by the film will interrupt the game. Ergo, there's some value to recording everything in RAM.

Or putting it another way, it's about all I can think of to fill up GBs of PS4 OS RAM, so Sony bloomin' well better be keeping the video in RAM!

 

[Betanumerical]

15*60=900 --> ~1MB/s.

cannot imagine any HDD having issues with that.

My understanding is that it is less of a bandwidth issue and more of a latency issue, introducing multiple even small or low bandwidth writes on a mechanical HDD will cause the heads to have move around (the distance of which depends on how far a away the two sections of data are) this would introduce read latency. What would have been a smart move with this would have been to include a hybrid drive with a small amount of ssd space and have the game scratch living there whilst the mechanical part of the drive is mass storage device for video etc. but that costs money.

 

[London Geezer]

No HDD would have trouble with that. However, almost all recorded material won't be saved, and every write to HDD by the film will interrupt the game. Ergo, there's some value to recording everything in RAM.

Or putting it another way, it's about all I can think of to fill up GBs of PS4 OS RAM, so Sony bloomin' well better be keeping the video in RAM!

I know you're half joking, but they really wouldn't need the whole video in RAM. Just enough as a buffer for when the game needs the HDD. Over a 15min period, I'd be very surprised if the system didn't have enough resources to dump part of the video from RAM to HDD, considering we're talking about MB per second kind of figures, out of pipes which hundreds of times larger.

 

[pMax]

My understanding is that it is less of a bandwidth issue and more of a latency issue

...find me a game which uses all your HDD bandwidth continually, without pauses.... that is, your red light stays on all time, your HD head scratches continually without any pause... latency, when you go to the HDD, is already there. Either you need the streamed data 1/2 second later, or you're screwed.

In any case, with PRT you can always show the lower res patch until the highres one comes...

 

[Shifty Geezer]

I know you're half joking, but they really wouldn't need the whole video in RAM. Just enough as a buffer for when the game needs the HDD. Over a 15min period, I'd be very surprised if the system didn't have enough resources to dump part of the video from RAM to HDD, considering we're talking about MB per second kind of figures, out of pipes which hundreds of times larger.

Yeah, RAM requirements is actually very little. We also discussed the possiblity of a flash cache in one of these threads (maybe even this one!). I suppose the balance would be more cache == more RAM used + less HDD writes. The sweet-spot would balance RAM use with minimising HDD impact.

 

[MrFox]

Great i/o schedulers hide this kind of thing almost completely, and the south bridge has 256MB of RAM, I assume it's where the i/o scheduling is handled, and where the buffer resides. It's hard to imagine a situation where it would cause a problem.

If they write the video to HDD, games that need continuous streaming of assets would need to give back only 2x seek + bandwidth time for every video block.

Assuming they put the video segment at the center of the HDD stroke, they'd get a bandwidth around 60MB/s and two seeks of 12ms.

With a 1MB buffer the game needs to accept a 40ms hiccup every second from the HDD.
With a 10MB buffer that would be 190ms every 10 seconds.

It's not so bad?

 

[Globalisateur]

Great i/o schedulers hide this kind of thing almost completely, and the south bridge has 256MB of RAM, I assume it's where the i/o scheduling is handled, and where the buffer resides. It's hard to imagine a situation where it would cause a problem.

If they write the video to HDD, games that need continuous streaming of assets would need to give back only 2x seek + bandwidth time for every video block.

Assuming they put the video segment at the center of the HDD stroke, they'd get a bandwidth around 60MB/s and two seeks of 12ms.

With a 1MB buffer the game needs to accept a 40ms hiccup every second from the HDD.
With a 10MB buffer that would be 190ms every 10 seconds.

It's not so bad?

That is pretty much how I always imagined PS4 dealt with the DVR task.

I wonder if the continuous background download/install of the PS4 takes more latency from the HDD than the DVR task. We know PS4 has an ARM + 256MB of DDR3 to do that but it must still take a lot of latency time from the HDD.

No wonder Sucher Punch specifically complained about slow IO access on PS4.

Maybe developers can interrupt (or limit) the background download/install of the PS4 like it was possible (by the developers?) to stop the single background download of the PS3 seen in some games.

 

[3dilettante]

Sucker Punch would have complained about slow IO even without network downloads or recording functionality, because the consoles are using cheap laptop mechanical drives.

 

[pMax]

Maybe developers can interrupt (or limit) the background download/install of the PS4

if I recall correctly, the low power ARM chip works when the console is turned off/not used, not when it is turned on and running the game.

Also, didnt it have 512mb of ram?

 

[MrFox]

if I recall correctly, the low power ARM chip works when the console is turned off/not used, not when it is turned on and running the game.

Also, didnt it have 512mb of ram?

No it's only 256MB.
It runs all the time, it basically alleviates all i/o tasks for the entire system. It would be logical that it's responsible for the buffering and scheduling, which should be inclusive in Cerny's wording: "manages all HDD access".

Cerny: The second custom chip is essentially the Southbridge. However, this also has an embedded CPU. This will always be powered, and even when the PS4 is powered off, it is monitoring all IO systems. The embedded CPU and Southbridge manages download processes and all HDD access. Of course, even with the power off.

 

[Shifty Geezer]

if I recall correctly, the low power ARM chip works when the console is turned off/not used, not when it is turned on and running the game.

I'm not sure it's ever been talked about in detail, but I'd expect the ARM processor to be constantly active running whatever tasks it does, such as downloading in standby or in the background.

 

[Globalisateur]

if I recall correctly, the low power ARM chip works when the console is turned off/not used, not when it is turned on and running the game.

Also, didnt it have 512mb of ram?

Thanks to the ARM+256mb of DDR3 the console can download in the background multiple files (something like at least 8 simultaneous downloads) + update & patching while playing.

 

[London Geezer]

Thanks to the ARM+256mb of DDR3 the console can download in the background multiple files (something like at least 8 simultaneous downloads) + update & patching while playing.

I did notice that. The Ps4 doesn't queue downloads like the PS3 used to do. If you have more than one download, they will all be happening at once. Not sure I prefer it to be honest. I'm sure I could pause some and let the one I want to play first for at full speed, and leave the others for later. Surely? Hasn't been a problem yet.

 

[JPT]

I did notice that. The Ps4 doesn't queue downloads like the PS3 used to do. If you have more than one download, they will all be happening at once. Not sure I prefer it to be honest. I'm sure I could pause some and let the one I want to play first for at full speed, and leave the others for later. Surely? Hasn't been a problem yet.

Question I have then, why would you not like it?

For home broadband devices, depending on your link speed, you will get better utilization when doing multiple downloads than just one. Due to your router using a dual-core cpu (most newer ones are multicore).

I have not investigated the traffic going to/from the PS4, but I assume it prioritizes game traffic over background download traffic when you are playing....

 

[Lalaland]

15*60=900 --> ~1MB/s.

cannot imagine any HDD having issues with that.

PDF Specsheet for PS4 hdd

Buffering to RAM may be a better option as I would imagine problem isn't the transfer rate penalty but the IOPS and drive head seek latency penalties. Constantly grabbing the drive head to write video data to the drive would impose random latency costs on reads for loading game data by yanking the drive head all over the drive. From what I can find 5400rpm drives are generally in the 50-100 IOPS range which isn't a whole lot to spare to write the last 15 mins of video over and over again.

I don't know the file system used in the next gen consoles but I would imagine they would be optimised to write game data contiguously for better read performance and lower seek latency. I know disc based games certainly employ this because of the far higher seek time for the laser in an optical drive.

The above is all speculation but writing constantly to disc just doesn't seem like a good idea. The PS4 does have a drive access light but that's not much help as it's almost always lit during a game anyway and also very small and dim.

EDIT: Guess who missed the whole next page discussing this very thing?

 

[Grall]

Constantly grabbing the drive head to write video data to the drive would impose random latency costs on reads for loading game data by yanking the drive head all over the drive.

If the data rate is a mere 1MB/s it's not much of an issue either on PS4 RAM or the HDD buffering 10 seconds' worth of video and writing it to disk all at once. It's a few tenths of a second access time (maybe counting high), about a tenth's worth of a second write time, another seek, and loading continues. You would never notice this ocurring every 10 seconds, not in a million years. Especially as drives commonly employ write caching and such trickery to try and hide seek penalties.

The PS4 does have a drive access light

...It does? Where?

 

[pMax]

...It does? Where?

...here, I suppose :smile: (if the pic is the real devkit, the site was not sure about...)

 

[London Geezer]

Question I have then, why would you not like it?

For home broadband devices, depending on your link speed, you will get better utilization when doing multiple downloads than just one. Due to your router using a dual-core cpu (most newer ones are multicore).

I have not investigated the traffic going to/from the PS4, but I assume it prioritizes game traffic over background download traffic when you are playing....

I do like it if I'm playing something and downloading something on the background. If I'm not, I'd like - and I'm sure there's a way - to get the first one out of the way as quickly as possible, then start playing and leave the others to finish.

 

[Lalaland]

If the data rate is a mere 1MB/s it's not much of an issue either on PS4 RAM or the HDD buffering 10 seconds' worth of video and writing it to disk all at once. It's a few tenths of a second access time (maybe counting high), about a tenth's worth of a second write time, another seek, and loading continues. You would never notice this occurring every 10 seconds, not in a million years. Especially as drives commonly employ write caching and such trickery to try and hide seek penalties.

But caching trickery depends on data locality and the writes will not be in the same sectors as the reads unless the file system is just plain ignoring the risks of fragmentation. It's not a huge time penalty writing but if your cache starts to overflow due to a large read job then you have to interrupt the read job to purge the cache slowing loading. The main issue I would see being the unpredictable nature of any latency or slow down it causes. Developers would be left wondering if that occasional geometry or texture pop in was an engine issue or just the 'Share' feature poking it's nose in.

It does? Where?

Damn I plainly suffer from the crazy, it isn't there but I'd have bet $20 it was to the right of the power switch until you pointed out my error!

 

[hesido]

I do wonder if PS4 downloads effect the network performance of multiplayer games, I'm thinking it should indeed have some prioritization for games.

I'd indeed like a pause button but I wouldn't like developers to stop my downloads. That also undermines Sony's reasoning to add the extra hardware, and everybody expects for their downloads to resume. I should be able to keep on playing BF4 even when I'm downloading the next 10GB game. I remember not being able to play some games on PS3 just because that game (even the single player part) blocked downloads, because I wanted the downloads to finish.

If they allow games to stop downloads entirely, my uneducated guess would be that most devs may choose to block downloads at the first sight of any problem to reduce the amount of variables that may be causing the problem.