Re: [PATCHv3 0/4] Improve fallback LPJ calculation
From: Stephen Boyd
Date: Fri Mar 18 2011 - 18:40:37 EST
On 03/10/2011 06:48 AM, Phil Carmody wrote:
> Apologies for picking on you, Andrew, and sending this out of the blue,
> but I didn't have much luck with my previous attempt, and I quite like
> this patchset, so thought it was worth trying again.
> The guts of this patchset are in patch 2/4. The motivation for that patch
> is that currently our OMAP calibrates itself using the trial-and-error
> binary chop fallback that some other architectures no longer need to
> perform. This is a lengthy process, taking 0.2s in an environment where
> boot time is of great interest.
> 1/4 is simply cosmetic to prepare for 2/4.
> 4/4 is simply to assist testing and not intended for integration.
I tried this patch set out on an MSM7630.
Calibrating delay loop... 681.57 BogoMIPS (lpj=3407872)
Calibrating delay loop... 680.75 BogoMIPS (lpj=3403776)
But the really good news is calibration time dropped from ~247ms to
~56ms. Sadly we won't be able to benefit from this should my udelay
patches make it into ARM because we would be using
calibrate_delay_direct() instead (at least on machines who choose to).
Can we somehow reapply the logic behind this to
calibrate_delay_direct()? That would be even better, but this is
definitely a boot time improvement.
Or maybe we could just replace calibrate_delay_direct() with this
fallback calculation? If __delay() is a thin wrapper around
read_current_timer() it should work just as well (plus patch 3 makes it
handle SMIs). I'll try that out.
You can add a
Tested-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
to the first 3 patches.
Sent by an employee of the Qualcomm Innovation Center, Inc.
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