Re: xennet slow under -current

[Brian Marcotte <marcotte%panix.com@localhost>]

>   * Input wasn't great in 9.1, but in -current, it's even slower.
> 
>     O/S     type    int      out       in (MBits/s)
>     ------- ----    -----   ----    -----
>     9.1     PV      xennet  1900      300
>     current PV      xennet  1960       45

For this problem, it looks like it appeared on April 11, 2020.

A list of the changed files is below. Notably there was a large change
to if_xennet_xenbus.c by jdolecek.

- Brian

--------------
common/lib/libc/gen/radixtree.c
sys/arch/i386/conf/XEN3PAE_DOM0
sys/arch/i386/conf/XEN3PAE_DOMU
sys/arch/macppc/dev/snapper.c
sys/arch/x86/include/cpu.h
sys/arch/x86/x86/cpu.c
sys/arch/x86/x86/patch.c
sys/arch/xen/include/xenbus.h
sys/arch/xen/x86/xen_bus_dma.c
sys/arch/xen/xen/hypervisor.c
sys/arch/xen/xen/if_xennet_xenbus.c
sys/arch/xen/xen/xbd_xenbus.c
sys/arch/xen/xen/xengnt.c
sys/arch/xen/xenbus/xenbus_probe.c
sys/dev/pci/pci_subr.c
sys/dev/pci/pcidevs
sys/dev/pci/pcidevs.h
sys/dev/pci/pcidevs_data.h
sys/dev/vnd.c
sys/kern/kern_condvar.c
sys/kern/kern_sleepq.c
sys/kern/subr_lockdebug.c
sys/kern/vfs_bio.c
sys/kern/vfs_cache.c
sys/kern/vfs_mount.c
sys/sys/buf.h
sys/sys/lockdebug.h
sys/sys/lwp.h
sys/sys/param.h
sys/uvm/uvm_map.c
sys/uvm/uvm_pdpolicy_clockpro.c