[U-Boot] OMAP3 performance regression in 2011.12

[Joe Woodward <jw@terrafix.co.uk>]

I'm fairly certain...

If I take the 2011.12 uBoot release the kernel takes about twice the time to boot (compared to 2011.09), and the device is noticably slower.

Then if I comment out the v7_out_cache_disable() line in cpu.c and rebuild uBoot then everything speeds up again.

I thought the kernel would turn on the cache again too...

Is there any easy way from userspace to determine if the cache is on?

I did a bit of Googling and found:
http://www.spinics.net/lists/arm-kernel/msg50083.html

It may be that the kernel is re-enabling the L1 cache, but expecting L2 to be on?
Or the way v7_out_cache_disable() disables L2 is not compatible with the way the kernel expects to re-enable it?

Cheers,
Joe

-----Original Message-----
From: Tom Rini <tom.rini@gmail.com>
To: Joe Woodward <jw@terrafix.co.uk>
Cc: u-boot at lists.denx.de
Date: Mon, 9 Jan 2012 08:11:07 -0700
Subject: Re: [U-Boot] OMAP3 performance regression in 2011.12

> On Mon, Jan 9, 2012 at 3:27 AM, Joe Woodward <jw@terrafix.co.uk> wrote:
> > Commit "armv7: disable L2 cache in cleanup_before_linux()" on 6th Dec
> 2011 by Aneesh V adds the following:
> >
> > arch/arm/cpu/armv7/cpu.c:cleanup_before_linux()
> >
> > ...
> > v7_out_cache_disable();
> > ...
> >
> > The commit message implies this change was to make booting reliable
> on OMAP4 by disabling L2 cache before jumping to Linux.
> >
> > However, when running with a stock 3.2 Linux kernel on an OMAP3 it
> has the effect of massively reducing system performance (when running
> using an OMAP3-
> > only 3.2 Linux Kernel on a GUSMTIX Overo OMAP3530).
> >
> > Therefore, I assume this means that the kernel isn't turning the L2
> cache back on for an OMAP3 (at least with my kernel build)!
> >
> > So, my question is...
> >
> > Are there any Kconfig options in Linux that will re-enable the L2
> cache (something obvious that I've missed), or is this commit just
> bad-news for OMAP3?
> 
> Are you certain that this is the commit that's causing your problem?
> The kernel is responsible for turning the cache back on and has for a
> long time, iirc.
> 
> -- 
> Tom