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869b44211a
Protect the reference point for kvmclock with a seqcount, so that kvmclock updates for all vCPUs can proceed in parallel. Xen runstate updates will also run in parallel and not bounce the kvmclock cacheline. Of the variables that were protected by pvclock_gtod_sync_lock, nr_vcpus_matched_tsc is different because it is updated outside pvclock_update_vm_gtod_copy and read inside it. Therefore, we need to keep it protected by a spinlock. In fact it must now be a raw spinlock, because pvclock_update_vm_gtod_copy, being the write-side of a seqcount, is non-preemptible. Since we already have tsc_write_lock which is a raw spinlock, we can just use tsc_write_lock as the lock that protects the write-side of the seqcount. Co-developed-by: Oliver Upton <oupton@google.com> Message-Id: <20210916181538.968978-6-oupton@google.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.