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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 12:59 pm

I voluteer at the National Museum of Computing, and luckily someone managed to pull some trings and get us a Pi ahead of schedule. So on Thursday they arrived and after a short trip to buy cables and SD cards, we soon had it fired up!

The point of this thread is for me to give just general feedback, I have been aware of the Raspberry Pi project, but I haven't been following it very closely so im sorry for any gaps in my knowledge, but hopefully it will provide you with the view point of a new user who has little previous knowledge of the project.

Our setup was quite funny because the only monitor we could find that had HDMI support was a 42" plasma TV, made quite a contrast to the tiny Pi! We also had a 4GB SD card with Debian Squeeze & LXDE on it.

Everything worked fine the first time we booted it up the only issue we had is we didn't know what the default password was! After a few frantic moments Googling, we figured it out the pi:suse login!

The Pi seemed really responsive and just like any other work station I have worked on before we started the Xserver. After playing around in the command line and poking some directories (I hadn't used Debian before, BSD man myself), we discovered that the bash history hadn't been wiped from the iso so we could see the previous commands used in creating the image (Just thought I should mention that).

We then fired up the Xserver, unsure of what DE had been installed and were enlighted by the brilliant blue LXDE  background on the 42" TV. This is where the Pi was starting to be strained, at idle the Xserver alone would be using 25% of the RAM and 5% of the CPU. What I would love to know is if the drain on the Xserver is increased by the size of the monitor? For instance if we had a small 15" display would it use up less resources?

Because of the large drain on resources powering the display the Pi became really rather slow, however for simple tasks it more than coped. However when I tried to open the Dropbox website to download some test programs the javascript heavy interface failed to load (In Midori). I then downloaded Ice-Weasel (firefox) and tried again with the same result.

After I put the code to the test program I was talking about in a pastebin and downloaded to the Pi I then compiled it quickly and got it calculating prime numbers. It seemed to handle that small C program I had written fairly well and calculated all the prime numbers under 100,000 in under a minute (plus a load of other calculations for the display) which was fairly good.

Now we are just trying to think of cool displays we can use the Pi in at the museum, I think the leading idea at the moment is to try and get C running on a BBC Micro so that we can run the same prime number program on both systems to see which is fastest!

Thanks for reading and I hope this has been helpful in some way! We really strongly hope to bakc the Pi foundation and get this fantastic hardware used to help more kids get into coding!

P.S. Install Vim by default

EDIT: There are a lot of pictures, but I don't have access to them right now, I will upload them soon though!

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 1:21 pm

the size of the screen will not make any differace to the speed.

you may be better off with the latest Debian image
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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 1:45 pm

You'll definitely be better off with the latest Debian - it's at http://www.raspberrypi.org/downloads. Really looking forward to seeing the pics!
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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 1:48 pm

Interesting to know about the X server speed, as it is currently accelerated (I'm working on hardware acceleration for this). Can you try scrolling up and down and moving windows around and stuff and see how you CPU load changes?

Cheers

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 2:00 pm

I wouldn't be at all surprised if the screen had an impact on performance: chances are a 42" screen is running at 1920 x 1080, rather than 1280 x 1024 of an old 4:3 monitor. So, you will be using more RAM for the display and pushing 50% more pixels.

I had exactly the same issue on a Mac mini when I switched to a 1080P monitor.

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 2:04 pm

It will be very interesting to see how that compares to the latest debian release!  That number should drop as the underlying GUI makes better use of the GPU
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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 3:37 pm

walney said:


I wouldn't be at all surprised if the screen had an impact on performance: chances are a 42" screen is running at 1920 x 1080, rather than 1280 x 1024 of an old 4:3 monitor. So, you will be using more RAM for the display and pushing 50% more pixels.

I had exactly the same issue on a Mac mini when I switched to a 1080P monitor.



It's NOT the Physical size, but the RESOLUTION of the display that matters...

Higher resolution = more pixels to render. More Pixels to render = more calculations that need to be performed to update the screen = slower performance.

A 50" 1080P display will work the same as a 15" 1080P display, since they both are 1920x1080 resolution.

Getting a 720P display will go faster because it's only 1920x720 resolution. Of course, you have lower res...

It amazes me that people STILL don't get the difference between screen PHYSICAL size and screen RESOLUTION!

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 4:22 pm

Don't forget colour depth... 8 bit colour is much faster than 32 bit.

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 4:48 pm

zardoz99 said:


Don't forget colour depth... 8 bit colour is much faster than 32 bit.


FYI The Raspi uses a 16bpp framebuffer.
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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 5:16 pm

Thanks a lot for your feed back guys, here are a couple of snapshots:









And of course the 42" TV is running at 1080P I should have mentioned that. Next time I can play with it (Probably Thursday) I will test out the performance at carying settings and levels of activity and report back to you

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 5:35 pm

mkopack said:


walney said:


I wouldn't be at all surprised if the screen had an impact on performance: chances are a 42" screen is running at 1920 x 1080, rather than 1280 x 1024 of an old 4:3 monitor. So, you will be using more RAM for the display and pushing 50% more pixels.

I had exactly the same issue on a Mac mini when I switched to a 1080P monitor.


It's NOT the Physical size, but the RESOLUTION of the display that matters...

...
It amazes me that people STILL don't get the difference between screen PHYSICAL size and screen RESOLUTION!


<sigh>

I am well aware of the difference between screen size and resolution. A good proportion of 15" monitors will run at 1280x1024 or lower (even new ones that you buy right now). With a 42" monitor, chances are it will be running at 1080p. So although the two (size and resolution) are not inextricably linked, bigger does tend to have higher resolution, consequently you might get a better visual impression using a lower resolution monitor.

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 6:15 pm

This has got me wondering. I'm not sure how big the framebuffer is on the Raspi. It might always  be 1080p and just scaled down to the correct size for the destination display. In which case it doesn't matter what size the display is, the fb performance is always the same. I'll need to check with Dom.
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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 7:08 pm

teh_orph said:


Interesting to know about the X server speed, as it is currently accelerated (I'm working on hardware acceleration for this). Can you try scrolling up and down and moving windows around and stuff and see how you CPU load changes?

Cheers



Did you mean " it is currently UNaccelerated"?

Otherwise I don't understand your posting!

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 7:23 pm

Hmmm… that jogs my memory: I think that Dom already answered this aeons ago…

http://www.raspberrypi.org/for.....onfig-txt/

Comment #42

So it looks like you are using:

arm192_start.elf : 192M ARM, 64M GPU split

which accounts for the 25% memory usage.

CPU may well be resolution dependent, especially with X not having hardware acceleration. Top should give you a better indication of what is eating your cpu.

[Edit: just wondering whether going down to the 224M ARM, 32M GPU might be doable on a lower screen resolution]

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 7:56 pm

The frambuffer (and so X resolution) will depend on the negotated resolution with display.

You can force it to be lower with, say:

framebuffer_width=1280

framebuffer_height=720

You get two benefits from a smaller framebuffer.

1) Less SDRAM bandwidth as the framebuffer is fetched for display. I think this equated to about 2% performance when running benchmarks, so not much.

2) The ARM has less pixels to fill when refreshing windows. That can be substantial when, say, scrolling a webpage, where the window fills the display. Time to redraw the window is roughly proportional to the number of pixels, so it may feel more responsive at 1280x720 rather than 1920x1080.

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 8:32 pm

arm2 said:


teh_orph said:


Interesting to know about the X server speed, as it is currently accelerated (I'm working on hardware acceleration for this). Can you try scrolling up and down and moving windows around and stuff and see how you CPU load changes?

Cheers


Did you mean " it is currently UNaccelerated"?

Otherwise I don't understand your posting!



Lollers, yes I'm missing the UN bit! I'm still interested in getting actual perf numbers from people who have the kit

Btw I could have sworn I saw a check-in comment (somewhere) about the framebuffer having been moved into main memory...

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 9:28 pm

This question has probably been asked before, but in view of the above comments what actually is the optimum resolution for a monitor, to get the most efficient (if that is the correct word to use here) performance from a Raspberry Pi... and the sharpest image too of course ?

Thanks.

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 9:34 pm

Well, the CPU and GPU do share "main memory" so yes.

By creating a "config.txt" file on the SD-Card you can control (amongst many other things) the screen resolution, and thus the number of pixels the CPU has to shift.

You can also choose how much RAM goes to the GPU, by renaming one of the "GPU binary blob files" (firmware for the GPU) to "boot.elf", there are normally three one for each memory split, with 32MB, 64MB or even 128MB going to the GPU, and only one is simply named "boot.elf", that is the one that is used. Each of them supports the maximum resolution, so that is not a reason to not chose the 32MB one, but playing video, or using 3D graphics is influenced by the amount of available GPU RAM.

By the way, a much cheaper solution than using a HDTV with an HDMI interface is using a ("VGA") monitor that happens to have a DVI input as well, as is the case with many monitors that are used as VGA monitors. Even fairly old ones came with a DVI-D interface connector, and you only need a cheap MDMI to DVI converter cable to use them. The PI will also "negotiate" with the monitor for the default resolution, so you might even see a speed increase when using an old monitor. Just look at the back of any old VGA monitor you have, if you see (next to the VGA input) another slightly larger (often white) one with one larger rectangular input slot you are in luck. Google for DVD-D pictures to see how the connector looks like. DVI-I connectors are also okay, but not the (quite rare) DVI-A connectors (which are missing a lot of pin holes in the middle of the connector, but see the google pics to be sure)

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 9:43 pm

Yeah I believe a colleague at the museum has just ordered some HDMI to DVI connectors, the TV is novel but really isn't practical!

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Re: Been playing with a Pi for the last couple of days. General comments!

Mon Apr 16, 2012 9:44 pm

Montala said:


This question has probably been asked before, but in view of the above comments what actually is the optimum resolution for a monitor, to get the most efficient (if that is the correct word to use here) performance from a Raspberry Pi... and the sharpest image too of course ?

Thanks.


Well most distro's work fine with an 800x600 resolution, and for a very long time that was also the optimum resolution for web-browsers (in my experience).

But its quite simple. The more pixels the CPU has to shift (copy to another location) the slower the result. That is, until the CPU gets some help from the (much more powerful) GPU. That is possible, but not implemented yet, but will hopefully come soon.

Sharpness of image results from a mix of display resolution, quality of the monitor, and how well the resolution that the R-PI drives the monitor at actually fits the capabilities of the monitor. The monitor might cope with a "wrong for it" resolution, but (for example) only by doubling every other pixel, which gives a very nasty effect!

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Re: Been playing with a Pi for the last couple of days. General comments!

Tue Apr 17, 2012 7:43 am

Montala said:


This question has probably been asked before, but in view of the above comments what actually is the optimum resolution for a monitor, to get the most efficient (if that is the correct word to use here) performance from a Raspberry Pi... and the sharpest image too of course ?

Thanks.


Well, the sharpest image is the native LCD resolution. But on a 1080p device (or larger) that means a lot of CPU work moving pixels. Dropping the size reduces sharpness, but increases speed. It's a very direct trade off of speed vs quality.
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Re: Been playing with a Pi for the last couple of days. General comments!

Tue Apr 17, 2012 11:07 pm

JamesH said:

FYI The Raspi uses a 16bpp framebuffer.
This seems quite a limitation.  Do you mean that the current firmware or drivers use a 16bpp framebuffer, or that the platform will only ever support a 16bpp framebuffer?

What about OGLES and H.264?  It is difficult to avoid visible banding or dithering with only 65536 colours, so I would hope they are 24bpp output?

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Re: Been playing with a Pi for the last couple of days. General comments!

Tue Apr 17, 2012 11:27 pm

It's just the default framebuffer (and it's programmable).

OGLES and H264 will be full colour.

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Re: Been playing with a Pi for the last couple of days. General comments!

Fri Apr 20, 2012 2:24 pm

Three of the photos were taken by Adam Bradley, another volunteer at the museum

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Re: Been playing with a Pi for the last couple of days. General comments!

Fri Apr 20, 2012 10:15 pm

Is there a recommended (max for practical purposes) resolution?  I'm thinking of connecting this Pi to a HDMI bigscreen as well.

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