[coreboot] Timing via serial port

Carl-Daniel Hailfinger c-d.hailfinger.devel.2006 at gmx.net
Sun Apr 19 11:33:42 CEST 2009

On 19.04.2009 07:02, Mart Raudsepp wrote:
> On L, 2009-04-18 at 23:05 -0400, Kevin O'Connor wrote:
>> On Sat, Apr 18, 2009 at 09:14:06PM -0400, Kevin O'Connor wrote:
>>> The biggest SeaBIOS time consumers:
>> [...]
>>> 425ms - scanning for option roms
>> I tracked this one down - it's the cost of CBFS and reading the flash.
>> Of the 425ms, 90ms is spent copying the via vga rom.  The remaining
>> time is spent doing CBFS searches - there are 18 pci devices on this
>> machine and for each one SeaBIOS scans CBFS for "pciVVVV,DDDD.rom".
>> Because none of these files were actually present, SeaBIOS ended up
>> walking all the flash freespace each time.  All those flash accesses
>> add up.
> Is there no zero-fill with cbfs?
> With LAR if I don't zero-fill (add a dummy entry to fill up the
> remaining space, the content is actually 0xFF's despite the term) it
> will also walk all the flash free space.
> Observing roughly 1 sec vs 4 sec boot times with and without zero-fill -
> I need to make a proper measurement, and this kind of tools that you and
> Peter have written were exactly what I was missing for doing that!
> In coreboot-v3 there's a Kconfig option to zero-fill, but as I have to
> manually add the Geode VSA blob, I have that disabled and do it manually
> as described in http://www.coreboot.org/Artec_Group_DBE62
> However I don't think zero-fill was even the default option in v3.
> Maybe you can do zero-fill entry for cbfs too similarly.

Not yet.

> I believe Carl-Daniel mentioned CBFS doesn't fix that problem either and
> shares the gotcha with LAR at the moment still.

Replace CBFS with zerofilled LAR and the problem will go away without
having to code another feature.



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