carbone
Posts: 52
Joined: Tue Jul 16, 2019 6:09 pm
Location: Sheffield UK

Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Tue Feb 11, 2020 10:35 pm

Since the latest boot_loader update I can no longer boot at arm_freq=2000 but if I drop to arm_freq=1980 I can boot and change back to arm_freq=2000 I can reboot and reboot many times with no problems until the next cold boot. What could be the cause of this behaviour?

Puffergas
Posts: 36
Joined: Thu Dec 19, 2019 12:16 am

Re: Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Wed Feb 12, 2020 1:06 am

I do not adjust the freq., however I have noticed that reboots do no longer work. Need to shutdown and then cycle the power switch. Otherwise, just two multi color square boxes. I think the green LED flashes seven times. It flashes fast so a wee bit hard to count.

carbone
Posts: 52
Joined: Tue Jul 16, 2019 6:09 pm
Location: Sheffield UK

Re: Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Fri Feb 14, 2020 2:57 pm

carbone wrote:
Tue Feb 11, 2020 10:35 pm
Since the latest boot_loader update I can no longer boot at arm_freq=2000 but if I drop to arm_freq=1980 I can boot and change back to arm_freq=2000 I can reboot and reboot many times with no problems until the next cold boot. What could be the cause of this behaviour?
I have since tried arm_freq=2020 and it will cold boot. I then tried arm_freq=2001and it will cold boot . All are with over_voltage=6.

Is it the way the PLL is being used for the DVFS firmware that prevents cold booting with a very specific arm_freq?

ejolson
Posts: 4278
Joined: Tue Mar 18, 2014 11:47 am

Re: Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Fri Feb 14, 2020 3:07 pm

carbone wrote:
Fri Feb 14, 2020 2:57 pm
carbone wrote:
Tue Feb 11, 2020 10:35 pm
Since the latest boot_loader update I can no longer boot at arm_freq=2000 but if I drop to arm_freq=1980 I can boot and change back to arm_freq=2000 I can reboot and reboot many times with no problems until the next cold boot. What could be the cause of this behaviour?
I have since tried arm_freq=2020 and it will cold boot. I then tried arm_freq=2001and it will cold boot . All are with over_voltage=6.

Is it the way the PLL is being used for the DVFS firmware that prevents cold booting with a very specific arm_freq?
Have you verified using any benchmark tool to check that the clock speeds you specify actually change the performance in a measurable way?

carbone
Posts: 52
Joined: Tue Jul 16, 2019 6:09 pm
Location: Sheffield UK

Re: Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Fri Feb 14, 2020 3:14 pm

It is blindingly obvious with web browsing and iPlayer that performance at 2000 is far better than at 1500. Real world is more important than an arbitrary benchmark.

The point of the post was not about obtaining any particular clock but what was preventing the cold booting at 2000.

ejolson
Posts: 4278
Joined: Tue Mar 18, 2014 11:47 am

Re: Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Fri Feb 14, 2020 3:37 pm

carbone wrote:
Fri Feb 14, 2020 3:14 pm
It is blindingly obvious with web browsing and iPlayer that performance at 2000 is far better than at 1500. Real world is more important than an arbitrary benchmark
I'll take that as a no, then.

There was an incident not so long ago of a different SOC that was reporting clock speeds much higher than the processor was actually running. Since the apparent speed of a browser depends on network, storage and video performance as well as the particular website being visited, it makes sense to check if the reason the Pi boots at odd clock speeds is because those speeds are being rounded down to a reasonable failsafe.

carbone
Posts: 52
Joined: Tue Jul 16, 2019 6:09 pm
Location: Sheffield UK

Re: Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Fri Feb 14, 2020 3:40 pm

Have you actually read my posts! The point is that since the latest bootloader I can no longer cold boot with arm_freq=2000 in /boot/config.txt but can warm boot and can still cold boot with arm_freq=2001 in /boot/config.txt. I don't care if the arm frequency is being misreported or not. I was merely enquring in a "General Discussion" forum if anyone knew the reason for this "new" behaviour. I will not lose any sleep if nobody explains.
vcgencmd measure_clock arm
frequency(48)=2001480448
vcgencmd measure_volts core
volt=1.0441V
Last edited by carbone on Fri Feb 14, 2020 3:57 pm, edited 2 times in total.

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 25002
Joined: Sat Jul 30, 2011 7:41 pm

Re: Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Fri Feb 14, 2020 3:43 pm

`vcgencmd measure_clock arm` will tell you exactly what speed the arm cores are running at.

As for this specific issue, odd one. There have been some reports of failures to sudo reboot, but rebooting correctly on power down/up. But no-one has been mentioning overclocking, as per this issue. So not sure. Just feel fortunate you can get a stable system over 2000, because that a very good overclock?
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
“I own the world’s worst thesaurus. Not only is it awful, it’s awful."

ejolson
Posts: 4278
Joined: Tue Mar 18, 2014 11:47 am

Re: Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Fri Feb 14, 2020 3:51 pm

carbone wrote:
Fri Feb 14, 2020 3:40 pm
Have you actually read my posts!
From what I read, you appear to be changing config.txt and then checking whether the Pi still boots. My thought is to further check by how much the Pi is faster after each change.

Maybe the Pi 4B really can run at 2GHz. There are definitely other ARMv8 cores which do this by default. At the same time, a reliable 30% overclock does not sound plausible to me. That is why I would be interested in a confirmation that the number 2001 isn't simply being rounded down to 1650 or something.

pica200
Posts: 181
Joined: Tue Aug 06, 2019 10:27 am

Re: Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Fri Feb 14, 2020 4:57 pm

2 GHz has been working since Pi 4 launch but it was and never will be 100% stable because of the PMIC.

The problems on reboot could be related to the recent bugs. Try fully updating Raspbian.

carbone
Posts: 52
Joined: Tue Jul 16, 2019 6:09 pm
Location: Sheffield UK

Re: Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Fri Feb 14, 2020 5:35 pm

Why don't people read what is actually posted! I am not complaining about stability, although I have not had any problems at 2GHz. It will run for days under normal usage but I haven't tried to stress test it. ( I do have Pimoroni fan shim.)

The inability to cold boot at exactly arm_freq=2000 occured after a full update of Raspbian, That is how I came to have the latest version of bootloader!

I was asking if there was anything special about arm_freq=2000 with the latest firmware? Could it be that it is a multiple of 500 the max core frequency but then 1500 is also a nultiple? Or some other reason?

I was also pointing out that with the new firmware the inability to cold boot at a particular frequency as in the past does not neccesarily mean the overclock potential has been reduced.

carbone
Posts: 52
Joined: Tue Jul 16, 2019 6:09 pm
Location: Sheffield UK

Re: Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Fri Feb 14, 2020 5:44 pm

Regarding stability I have also run Gentoo64 and run "genup" which has "emerged" over 300 packages with no problems.

pica200
Posts: 181
Joined: Tue Aug 06, 2019 10:27 am

Re: Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Fri Feb 14, 2020 10:09 pm

That doesn't mean anything as do synthetic benchmarks. Try the unsharpen filter with 2 GHz in Gimp on a large picture like the ones Raspbian comes with (backgrounds) and you will see what i mean.

I didn't notice any stability problems on cold boot with newest firmware.

carbone
Posts: 52
Joined: Tue Jul 16, 2019 6:09 pm
Location: Sheffield UK

Re: Why since DVFS firmware can I reboot at a higher arm_freq than from a cold boot?

Fri Feb 14, 2020 10:59 pm

I am not complaining about instability, that red herring was introduced by others. ,

With
[email protected]:~ $ sudo rpi-eeprom-update
BCM2711 detected
BOOTLOADER: up-to-date
CURRENT: Fri 17 Jan 17:37:11 UTC 2020 (1579282631)
LATEST: Fri 17 Jan 17:37:11 UTC 2020 (1579282631)
VL805: up-to-date
CURRENT: 000137ad
LATEST: 000137ad


With arm_freq=2000 I can no longer cold boot but I can warm reboot. So I thought the latest firmware has reduced my potential overclock.

With arm_freq=1980 I could cold boot and warm reboot.

After some thought I decided that the difference was so marginal I would have expected a "grey area" so I upped the frequency.

With arm_freq=2020 I could cold boot and warm reboot. so It is not the silicon. I thought I wondered if....

With arm_freq=2001 I could both cold and warm reboot so it is not the silicon or DVFS firmware in itself. I was just asking if anyone could give an explanation.

By the way I get the same behaviour with Gentoo64 with the same Bootloader but that is still running 24 Sept firmware. I can not find out how to update the vcgencmd version firmware in Gentoo64 which is still in /boot not eeprom.

Perhaps I should say that the cold boot hangs immediately after the the screen where you can press Shift if an overclock fails. I still get a resolution change reported by the TV being used as a monitor but no boot messages on the screen. I am using verbose for boot messages.

Return to “General discussion”