Warning about kernel 4.2 performance

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Hi all,
    I think it best to warn everyone that requires the maximum performance for Dosemu and is using 32bit linux to get hardware assistance via cpuemu=off (the default on 32bit), that if you install a 4.2 kernel or greater the system call that Dosemu uses to get you that extra speed is being turned off by default on upstream kernels. It is up to the individual distros to enable it specifically. This will, depending upon what your DOS app does, cause a considerable performance drop (for me that's about about a factor of 10) as Dosemu falls back to cpuemu=vm86. 

In Ubuntu Wily they have not enabled the vm86() system call, which I expect is because they overlooked the fact a new kernel config switch was added, which means if you need the speed you'll have to start building your own kernels. I raised a bug on Ubuntu's Launchpad tracker asking for the syscall to be compiled in, but runtime disabled by default and you should do the same for your distro if it's important to you too.

Andrew Bird <ajb@xxxxxxxxxxxxxxxxxxx>
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