From mboxrd@z Thu Jan 1 00:00:00 1970 From: mingo@elte.hu (Ingo Molnar) Date: Thu, 30 Apr 2009 17:01:42 +0200 Subject: [ltt-dev] [PATCH] Fix dirty page accounting in redirty_page_for_writepage() In-Reply-To: References: <20090429232546.GB15782@Krystal> <20090430024303.GB19875@Krystal> <20090430133859.GB8329@elte.hu> <20090430141446.GD14696@elte.hu> <20090430143819.GF14696@elte.hu> Message-ID: <20090430150142.GC20580@elte.hu> * Christoph Lameter wrote: > On Thu, 30 Apr 2009, Ingo Molnar wrote: > > > > Yes but sometimes you are already irq safe and such a fallback > > > would create significant irq/enable/disable stack operations etc > > > overhead for architectures that are using the fallback. > > > > It's a fallback slowpath - non-x86 architectures should still fill > > in a real implementation of course. > > Arch code cannot provide an effective implementation since they > always have to assume that interupts need to be disabled if we stay with > the current implementation. > > > So we first have to see the list of architectures that _cannot_ > > implement an irq-safe op here via a single machine instruction. > > x86, ia64 and powerpc should be fine. > > Look at Ia64, sparc, s/390, powerpc. They can fall back to atomic > ops but those are very ineffective on some of these platforms. > Since these are performance critical they will need to be > optimized depending on the context of their use in the core. Could you cite a specific example / situation where you'd use __xxx ops? Ingo