linux-kernel - Re: [PATCH] Revert 9fc2105aeaaf56b0cf75296a84702d0f9e64437b to fix pyaudio (and probably more)

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Date:	Wed, 7 Jan 2015 01:41:33 -0500 (EST)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Catalin Marinas <catalin.marinas@....com>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Pavel Machek <pavel@....cz>,
	Marc Zyngier <marc.zyngier@....com>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert 9fc2105aeaaf56b0cf75296a84702d0f9e64437b to fix
 pyaudio (and probably more)

On Tue, 6 Jan 2015, Catalin Marinas wrote:

> I think that's where the misunderstanding is. We don't have any idea
> how many times we go through the delay loop. We just go through the
> delay loop until the counter (driven by an independent frequency)
> changes X times. From arch/arm/lib/delay.c:
> 
> static void __timer_delay(unsigned long cycles)
> {
>         cycles_t start = get_cycles();
> 
>         while ((get_cycles() - start) < cycles)
>                 cpu_relax();
> }
> 
> where the number of cycles is based on the pre-calculated lpj_fine
> value using the counter/timer frequency (read from DT or hardware).
> 
> I think Nico already pointed out that the way we use loops_per_jiffy
> when the udelay is timer-based is probably wrong. We actually need a
> ticks_per_jiffy which has nothing to do with loops_per_jiffy, the
> former is actually completely independent from the CPU speed.

We already have the former.

The patch I posted rehabilitated thelater.  That's the sanest we can do.
Then we have both a timer based delay and a bogomips that is somewhat 
related to CPU speed again.

I also posted another patch to remove the 3355 bogomips limitation on 
ARM.


Nicolas
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