On Wed, Jul 13, 2016 at 12:53 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote: > > * Andy Lutomirski <luto@xxxxxxxxxx> wrote: > >> This allows x86_64 kernels to enable vmapped stacks. There are a >> couple of interesting bits. > >> --- a/arch/x86/Kconfig >> +++ b/arch/x86/Kconfig >> @@ -92,6 +92,7 @@ config X86 >> select HAVE_ARCH_TRACEHOOK >> select HAVE_ARCH_TRANSPARENT_HUGEPAGE >> select HAVE_EBPF_JIT if X86_64 >> + select HAVE_ARCH_VMAP_STACK if X86_64 > > So what is the performance impact? Seems to be a very slight speedup (0.5 µs or so) on my silly benchmark (pthread_create, pthread_join in a loop). It should be a small slowdown on workloads that create many threads all at once, thus defeating the stack cache. It should be a *large* speedup on any workload that would trigger compaction on clone() to satisfy the high-order allocation. > > Because I think we should consider enabling this feature by default on x86 - but > the way it's selected here it will be default-off. > > On the plus side: the debuggability and reliability improvements are real and > making it harder for exploits to use kernel stack overflows is a nice bonus as > well. There's two performance effects: Agreed. At the very least, I want to wait until after net-next gets pulled to flip the default to y. I'm also a bit concerned about more random driver issues that I haven't found yet. I suppose we could flip the default to y for a few -rc releases and see what, if anything, shakes loose. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
