[syslinux] Measuring boot time

[Gene Cumm]

On Wed, Jul 8, 2015 at 12:47 AM, Tal Lubko <tallubko at yahoo.com> wrote:
> Hi Gene
>
> Thanks for your reply.
> I'm trying to breakdown overall system boot time and to understand each
> component duration.
> My linux image is a ~10 MB bzImage file with the rootfs cpio'ed inside.
>
> I also have 2 BIOS images:
> - some general purpose BIOS
> - a custom BIOS which loads real quick
>
> I'm using TSC to measure time. I'm not sure it's the best way (I've read
> about CPU's synchronization problems with it) but I'm not sure how to do it
> otherwise.

Syslinux is essentially a single-core single-thread application.
Unless your BIOS uses other cores for some BIOS function calls, they
shouldn't matter.

> I've added the following TSC reads at:
> 1) the begining of a custom c32 module which later calls
> "syslinux_run_command"
> 2) the begining of "start_kernel" function
> 3) end of kernel load
>
> As far as I understand the duration between 1 to 2 is bootloader time (am I
> wrong?).

That sounds reasonable.  Time to fetch kernel and iniitrd payload(s)
plus set it all up.

> Using the custom BIOS:
> - it takes ~1.1 seconds for bootloader to finish
> - it takes ~0.9 seconds for Linux to finish
>
> Using the general purpose BIOS:
> - it takes ~0.45 seconds for bootloader to finish
> - it takes ~0.9 seconds for Linux to finish
>
> Of course that the overall boot time with the general purpose BIOS is much
> longer than with the custom BIOS (the custom BIOS is intended to cut down
> boot time).
>
> So I'm trying to understand:
> - Where does the extra bootloader time go when using the custom BIOS?

Any of various sources though most likely your custom BIOS is just
slower at its disk access.

> - Is there a mechanisem built into syslinux code which can help solve this
> mystery?

There's not any mechanism that I know of aside from using cptime.c32
to time how long it takes for the files to be loaded or enabling some
of the debug functionality (with debug.c32 to the screen or a
recompile to output to a serial port at IO port 3F8h at 115200 8n1).

There are some obvious questions that are yet unanswered:

1) What version?  Where did it come from?

2) Where is it installed?  SYSLINUX on a hard drive or perhaps
installed to a USB drive of some sort?  Some USB BIOSs are horribly
slow.  Perhaps ISOLINUX on a CD or hybridized to a hard drive or USB
drive?

3) If SYSLINUX, what 3-character mode does the version/copyright
banner display, CHS or EDD?

-- 
-Gene

> ________________________________
> From: Gene Cumm <gene.cumm at gmail.com>
> To: Tal Lubko <tallubko at yahoo.com>
> Cc: "syslinux at zytor.com" <syslinux at zytor.com>
> Sent: Wednesday, July 8, 2015 4:45 AM
> Subject: Re: [syslinux] Measuring boot time
>
> On Mon, Jul 6, 2015 at 1:01 PM, Tal Lubko via Syslinux
>
>
>
> <syslinux at zytor.com> wrote:
>> Hello Everyone
>> I'd like to know what's the best way to measure syslinux functions
>> duration.I know how to measure overall time (from syslinux start), but is
>> there an easy way to break it down?
>
>
> What do you mean?  How long it takes to load individual files along
> the way from initial start to the kernel handoff?  cptime.c32 might
> offer a way to get some answers there.
>
> Do you mean how long individual function calls take?  That sounds like
> a non-trivial question if this is the case.