On Fri, Apr 29, 2016 at 10:01:08AM +0300, Matwey V. Kornilov wrote: > 2016-04-29 1:18 GMT+03:00 Richard W.M. Jones <rjones@xxxxxxxxxx>: > > [This is an opinionated patch, mainly for discussion.] > > > > I'm trying to reduce the time taken in the kernel in initcalls, with > > my aim being to reduce the current ~700ms spent in initcalls before > > userspace, down to something like 100ms. All times on my Broadwell-U > > laptop, under virtualization. The purpose of this is to be able to > > launch VMs around containers with minimal overhead, like Intel Clear > > Containers, but using standard distro kernels and qemu. > > > > Currently the kernel spends 25ms inspecting the UART that we passed to > > it from qemu to find out whether it's an 8250/16550/16550A perhaps > > with a non-working FIFO or other quirks. Well, it isn't -- it's a > > working emulated 16550A, with a FIFO and no quirks, and if it isn't, > > we should fix qemu. > > > > So the patch detects if we're running virtualized (perhaps it should > > only check for qemu/KVM?) and if so, shortcuts the tests. > > Does anybody know, whether it is possible to pass through real > hardware serial port to a guest? It seems to be as simple as to pass > through an interrupt and memory IO ports. In theory it seems like something VFIO could do. Passing something as low performance as a serial port through would seem to make little sense though. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-builder quickly builds VMs from scratch http://libguestfs.org/virt-builder.1.html -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
