From mboxrd@z Thu Jan 1 00:00:00 1970 From: grygorii.strashko@ti.com (Grygorii Strashko) Date: Sat, 5 Sep 2015 00:46:37 +0300 Subject: [PATCH v2 7/7] ARM: smp: Add runtime PM support for CPU hotplug In-Reply-To: References: Message-ID: <55EA113D.9000806@ti.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 09/04/2015 09:45 PM, Alan Stern wrote: > On Fri, 4 Sep 2015, Grygorii Strashko wrote: > >> There is one "small" problem with such approach :( >> >> - It's incompatible with -RT kernel, because PM runtime can't be used >> in atomic context on -RT. > > Can you explain this more fully? Why can't runtime PM be used in > atomic context in the -rt kernels? > See: http://lwn.net/Articles/146861/ https://rt.wiki.kernel.org/index.php/Frequently_Asked_Questions#How_does_the_CONFIG_PREEMPT_RT_patch_work.3F spinlock_t Critical sections are preemptible. The _irq operations (e.g., spin_lock_irqsave()) do -not- disable hardware interrupts. Priority inheritance is used to prevent priority inversion. An underlying rt_mutex is used to implement spinlock_t in PREEMPT_RT. As result, have to do things like: https://lkml.org/lkml/2015/8/18/161 https://lkml.org/lkml/2015/8/18/162 Sorry for brief reply - Friday/Sat night :) -- regards, -grygorii