[PATCH 0/6] Get rid of CPUID from gettimeofday

Alok Kataria akataria at vmware.com
Tue Jun 3 23:28:47 UTC 2008


There have been a series of patches committed to the mainline kernel
recently that address a performance issue for gettimeofday when running
on hypervisors that enable hardware assisted virtualization.  The
non-ideal performance occurs because a CPUID instruction is used to
serialize the pipeline before RDTSC, and when using hardware
virtualization, CPUID always exits to the hypervisor.

The code in question also exists in the ubuntu-hardy tree.

The fix is to use MFENCE/LFENCE instead of CPUID.
This series of patches backports those commits for current ubuntu's git

Please have a look. 


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