Each vCPU core exposes its timebase frequency in the DT. When running
under KVM, this means parsing /proc/cpuinfo in order to get the timebase
frequency of the host CPU.
The parsing appears to slow down the boot quite a bit with higher number
of cores:
# of cores seconds spent in spapr_dt_cpus()
8 0.550122
16 1.342375
32 2.850316
64 5.922505
96 9.109224
128 12.245504
256 24.957236
384 37.389113
The timebase frequency of the host CPU is identical for all
cores and it is an invariant for the VM lifetime. Cache it
instead of doing the same expensive parsing again and again.
Rename kvmppc_get_tbfreq() to kvmppc_get_tbfreq_procfs() and
rename the 'retval' variable to make it clear it is used as
fallback only. Come up with a new version of kvmppc_get_tbfreq()
that calls kvmppc_get_tbfreq_procfs() only once and keep the
value in a static.
Zero is certainly not a valid value for the timebase frequency.
Treat atoi() returning zero as another parsing error and return
the fallback value instead. This allows kvmppc_get_tbfreq() to
use zero as an indicator that kvmppc_get_tbfreq_procfs() hasn't
been called yet.
With this patch applied:
384 0.518382
Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <161600382766.1780699.6787739229984093959.stgit@bahia.lan>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
9cbcfb5924