Messages in this thread | | | Date | Wed, 29 Nov 2006 15:05:44 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] i386 add idle notifier |
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On Wed, 29 Nov 2006 14:18:53 -0800 Stephane Eranian <eranian@hpl.hp.com> wrote:
> Hello, > > On Wed, Nov 29, 2006 at 01:09:44PM -0800, Andrew Morton wrote: > > On Wed, 29 Nov 2006 17:09:39 +0000 > > Christoph Hellwig <hch@infradead.org> wrote: > > > > > On Wed, Nov 29, 2006 at 08:25:40AM -0800, Stephane Eranian wrote: > > > > Hello, > > > > > > > > Here is a patch that adds an idle notifier to the i386 tree. > > > > The idle notifier functionalities and implementation are > > > > identical to the x86_64 idle notifier. We use the idle notifier > > > > in the context of perfmon. > > > > > > > > The patch is against Andi Kleen's x86_64-2.6.19-rc6-061128-1.bz2 > > > > kernel. It may apply to other kernels but it needs some updates > > > > to poll_idle() and default_idle() to work correctly. > > > > > > Walking through a notifier chain on every single interrupt (including > > > timer interrupts) seems rather costly. What do you need this for > > > exactly? > > > Let me give you the background on this. > > In system-wide mode, perfmon wants to exclude useless kernel execution > from being monitored. That execution is performed by the idle thread > when it enters its lowest loop level, i.e., poll_idle(), defaut_idle(), > mwait_idle(). It used to be that the idle loop was simply looping, waiting > for an interrupt or polling a variable. These days, it is a bit more > complex because on many processors, idle means going to a lower power state. > We want to capture useful idle thread execution such as interrupt servicing > but we want to exclude polling and low-power state.
An alternative approach might be to change perfmon so that it works out whether it is being called by an idle thread
if ((current->flags & PF_IDLE) && (other stuff to do with irqs?)) return;
> We would still need the test_and_set > to avoid a race with interrupts.
btw, I don't think anyone promised that __test_and_set_bit is atomic wrt interrupts on all architectures. Is OK for x86.
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