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8644f771e0
Turns out Hyper-V on KVM (as of 2016) will only use synthetic timers if direct mode is available. With direct mode we notify the guest by asserting APIC irq instead of sending a SynIC message. The implementation uses existing vec_bitmap for letting lapic code know that we're interested in the particular IRQ's EOI request. We assume that the same APIC irq won't be used by the guest for both direct mode stimer and as sint source (especially with AutoEOI semantics). It is unclear how things should be handled if that's not true. Direct mode is also somewhat less expensive; in my testing stimer_send_msg() takes not less than 1500 cpu cycles and stimer_notify_direct() can usually be done in 300-400. WS2016 without Hyper-V, however, always sticks to non-direct version. Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Reviewed-by: Roman Kagan <rkagan@virtuozzo.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.