* Rusty Russell ([EMAIL PROTECTED]) wrote: > On Wednesday 14 November 2007 05:58:05 Mathieu Desnoyers wrote: > > x86 optimization of the immediate values which uses a movl with code > > patching to set/unset the value used to populate the register used as > > variable source. > > For the record, I think the patching code gross overkill. > > A stop_machine (or lightweight variant using IPI) would be sufficient and > vastly simpler. Trying to patch NMI handlers while they're running is > already crazy. >
I wouldn't mind if it was limited to the code within do_nmi(), but then we would have to accept potential GPF if A - the NMI or MCE code calls any external kernel code (printk, notify_die, spin_lock/unlock, die_nmi, lapic_wd_event (perfctr code, calls printk too for debugging)... B - we try to patch this code at the wrong moment I could live with that, but I would prefer to have a solid, non flaky solution. My goal is to help the kernel quality _improve_ rather than deteriorate. Therefore, if one decides to use the immediate values to leave dormant spinlock instrumentation in the kernel, I wouldn't want it to have undesirable side-effects (GPF) when the instrumentation is being enabled, as rare as it could be. > I'd keep this version up your sleeve for they day when it's needed. > If we choose to go this way, stop_machine would have to do a sync_core() on every CPU before it reactivates interrupts for this to respect Intel's errata. It's not just a matter of not executing the code while it is modified; the issue here is that we must insure that we don't have an incoherent trace cache. So, as is, stop_machine would not respect the errata. Mathieu > Rusty. -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
