From mboxrd@z Thu Jan 1 00:00:00 1970 From: balbi@ti.com (Felipe Balbi) Date: Wed, 3 Jun 2015 16:28:21 -0500 Subject: [RFC/NOT FOR MERGING] HACK: add global/private timers for A9 In-Reply-To: <20150603210455.GD6042@saruman.tx.rr.com> References: <1433363565-17725-1-git-send-email-balbi@ti.com> <2466648.WjMxjIpAUG@wuerfel> <20150603210455.GD6042@saruman.tx.rr.com> Message-ID: <20150603212821.GH6042@saruman.tx.rr.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 -- balbi -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 819 bytes Desc: Digital signature URL: