From mboxrd@z Thu Jan 1 00:00:00 1970 From: arjan@linux.intel.com (Arjan van de Ven) Date: Wed, 21 Dec 2011 10:44:42 +0100 Subject: [PATCH 0/3] coupled cpuidle state support In-Reply-To: References: <1324426147-16735-1-git-send-email-ccross@android.com> <4EF1A0B4.5080307@linux.intel.com> Message-ID: <4EF1AA8A.8060304@linux.intel.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 12/21/2011 10:40 AM, Colin Cross wrote: >> this smells fundamentally racey to me; you can get an interrupt one >> cycle after you think you're done, but before the last guy enters WFI... >> >> how do you solve that issue ? > > All the cpus have interrupts off when they increment the counter, so > they cannot receive an interrupt. If an interrupt is pending on one > of those cpus, it will be handled later when WFI aborts due to the > pending interrupt. ... but this leads to cases where you're aborting before other cpus are entering..... so your "last guy in" doesn't really work, since while cpu 0 thinks it's the last guy, cpu 1 is already on the way out/out already... (heck it might already be going back to sleep if your idle code can run fast, like in the size of a cache miss)