On Fri, Apr 29, 2016 at 08:41:14AM +0100, Richard W.M. Jones wrote: > 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. Multi-port serial PCI cards are not "low performance" and might be passed through directly to a guest. thanks, greg k-h -- 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
