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Re: m68k Installer performance and kernel profiling (was: Updated installer images 2020-12-02)


On 1/3/21 1:38 AM, Finn Thain wrote:
On Sun, 3 Jan 2021, Eero Tamminen wrote:
* While kernel runs init a minute after being
   booted [1], installer is *much* slower.

   E.g. after pressing Enter to select another
   country, it takes 5-10 mins until installer
   presents me with a list from which I can select

Is that a kernel regression or an installer regression?

This is the first time I've run Debian kernel +
installer in Hatari, so I have no idea whether
it's a  regression. Sorry, I wasn't clear on that!

Based on some profiling I did, slowness is
completely on the user-space side. [1]

In cycles, memcpy() uses a bit more compared to
memset(), but memset() still takes most CPU.

Attached are partial callgraphs showing where
they're most called from.  Percentages in the
arrow lines indicate each function node's share
of those calls.

If this is a new phenomenon, git bisect may reveal what changed.

I've been testing upstream kernel boot times
since v5.2, and I don't think there's been any
significant regression...

Could the memcpy calls be related to 64-bit timekeeping?

...but if you're interested, I could profile and
provide similar callgraph for another kernel
you're interested about.  Just point me to kernel
+ initrd + symbols.map packages (or files) you'd
like me to check.

[1] There isn't any way to profile Linux user-
space in Hatari, except for having single number
of how much time whole user-space consumes
compared to kernel.

However, I can get very accurate profiling data
for all of the kernel side (depending on symbols
file content), and profiling whole Linux bootup is
trivial in Hatari.

Profiling kernel usage during specific user-
space activity would require that user-space
activity to start & end with call to some kernel
symbol/syscall that's not otherwise called
(so that emulator breakpoints can be set to
start and of the profiling).

	- Eero

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