On 06/03/2015 02:28 PM, Felipe Balbi wrote:
On Wed, Jun 03, 2015 at 04:04:55PM -0500, Felipe Balbi wrote:
On Wed, Jun 03, 2015 at 10:55:27PM +0200, Arnd Bergmann wrote:
On Wednesday 03 June 2015 15:32:45 Felipe Balbi wrote:
Hi Tony and Russell,
AM43xx, even though it's a single processor A9, it still has TWD and global
timer. I was doing some profiling with RT v4.0 and latency is 3.5x lower just
by switching from gptimer to twd/global.
The only problem is that currently, is_smp() check prevents me from using twd
with AM43xx (that's why it's commented below, for testing purposes).
In the hopes that we can start a, hopefully, small thread around the subject,
I'm sending this HACK which I used to get TWD and global timer enabled so I
could measure latencies with cyclictest.
Is it so that TWD shouldn't be available on UP integrations of ARM's Cortex-A
processors ?
I wondered about this recently when looking at something unrelated
and noticed that the check had been introduced as part of
904464b91eca8 ("ARM: 7655/1: smp_twd: make twd_local_timer_of_register()
no-op for nosmp").
I suspect this was just the wrong fix at the time, and that the
real culprit is either alloc_percpu() or request_percpu_irq()
getting called too early on a machine without SMP support.
Possibly the problem is already resolved independently, if you
didn't run into it.
no, no splats, nothing at all. See [1]
[1] http://hastebin.com/helekubutu
Adding Shawn
Mason was also interested in doing this. See [2]. From what I could tell
back then, commit 904464b91eca8 was working around the local timer APIs
that no longer exist.
[2] http://thread.gmane.org/gmane.linux.ports.arm.kernel/389931/focus=392348
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