* Gleb Natapov <gleb@xxxxxxxxxx> wrote: > On Mon, Nov 02, 2009 at 05:29:41PM +0100, Ingo Molnar wrote: > > > > * Gleb Natapov <gleb@xxxxxxxxxx> wrote: > > > > > On Mon, Nov 02, 2009 at 05:12:48PM +0100, Ingo Molnar wrote: > > > > > > > > * Gleb Natapov <gleb@xxxxxxxxxx> wrote: > > > > > > > > > On Mon, Nov 02, 2009 at 10:22:14AM +0100, Ingo Molnar wrote: > > > > > > > > > > > > * Gleb Natapov <gleb@xxxxxxxxxx> wrote: > > > > > > > > > > > > > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c > > > > > > > index f4cee90..14707dc 100644 > > > > > > > --- a/arch/x86/mm/fault.c > > > > > > > +++ b/arch/x86/mm/fault.c > > > > > > > @@ -952,6 +952,9 @@ do_page_fault(struct pt_regs *regs, unsigned long error_code) > > > > > > > int write; > > > > > > > int fault; > > > > > > > > > > > > > > + if (arch_handle_page_fault(regs, error_code)) > > > > > > > + return; > > > > > > > + > > > > > > > > > > > > This patch is not acceptable unless it's done cleaner. Currently we > > > > > > already have 3 callbacks in do_page_fault() (kmemcheck, mmiotrace, > > > > > > notifier), and this adds a fourth one. Please consolidate them into a > > > > > > single callback site, this is a hotpath on x86. > > > > > > > > > > > This call is patched out by paravirt patching mechanism so overhead > > > > > should be zero for non paravirt cases. [...] > > > > > > > > arch_handle_page_fault() isnt upstream yet - precisely what is the > > > > instruction sequence injected into do_page_fault() in the patched-out > > > > case? > > > > > > It is introduced by the same patch. The instruction inserted is: > > > xor %rax, %rax > > > > ok. > > > > My observations still stand: > > > > > > > [...] What do you want to achieve by consolidate them into single > > > > > callback? [...] > > > > > > > > Less bloat in a hotpath and a shared callback infrastructure. > > > > > > > > > [...] I mean the code will still exist and will have to be executed on > > > > > every #PF. Is the goal to move them out of line? > > > > > > > > The goal is to have a single callback site for all the users - which > > > > call-site is patched out ideally - on non-paravirt too if needed. Most > > > > of these callbacks/notifier-chains have are inactive most of the time. > > > > > > > > I.e. a very low overhead 'conditional callback' facility, and a single > > > > one - not just lots of them sprinkled around the code. > > > > looks like a golden opportunity to get this right. > > > Three existing callbacks are: kmemcheck, mmiotrace, notifier. Two > of them kmemcheck, mmiotrace are enabled only for debugging, should > not be performance concern. And notifier call sites (two of them) > are deliberately, as explained by comment, not at the function entry, > so can't be unified with others. (And kmemcheck also has two different > call site BTW) We want mmiotrace to be generic distro capable so the overhead when the hook is not used is of concern. Ingo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
