From: peterz@infradead•org (Peter Zijlstra)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] arm: spin one more cycle in timer-based delays
Date: Fri, 18 Nov 2016 15:42:10 +0100 [thread overview]
Message-ID: <20161118144210.GS3117@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <582F0DD2.3030805@free.fr>
On Fri, Nov 18, 2016 at 03:18:58PM +0100, Mason wrote:
> If I understand correctly, udelay is, in fact, a wrapper around
> several possible implementations. (Run-time decision on arch/arm)
>
> 1) The "historical" software loop-based method, which is calibrated
> during init.
>
> 2) A hardware solution, based on an actual timer, ticking away
> at a constant frequency.
I'd say clock, a timer would imply interrupts or somesuch, which is of
course not useful for udelay.
x86 with TSC uses this, although recent chips have grown an timed-mwait
instruction and that too can be used.
The TSC based ones (including the mwait) try very hard to not return
early.
> 3) others?
On x86 there's a variant that times itself based on io port accesses
which have a 'known' slowness.
next prev parent reply other threads:[~2016-11-18 14:42 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-15 13:36 [PATCH] arm: spin one more cycle in timer-based delays Mason
2016-11-18 12:06 ` Will Deacon
2016-11-18 12:24 ` Mason
2016-11-18 12:54 ` Russell King - ARM Linux
2016-11-18 14:18 ` Mason
2016-11-18 14:42 ` Peter Zijlstra [this message]
2016-11-18 17:51 ` Mason
2016-11-19 7:17 ` Afzal Mohammed
2016-11-19 11:03 ` Russell King - ARM Linux
2016-11-19 18:29 ` Mason
2016-11-20 19:18 ` Doug Anderson
2016-11-20 19:44 ` Russell King - ARM Linux
2016-11-20 20:00 ` Mason
2016-11-20 6:15 ` Afzal Mohammed
2016-11-20 19:15 ` Doug Anderson
2016-11-18 17:13 ` Doug Anderson
2016-11-18 17:32 ` Russell King - ARM Linux
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