tree 1c76da4dbb0ff5c2171dfa3c2e6834070014eb3c
parent 97ac984d2feec885d10f900591431088eab42021
author Suresh Siddha <suresh.b.siddha@intel.com> 1328581940 -0800
committer Ingo Molnar <mingo@elte.hu> 1329907780 +0100

x86/tsc: Reduce the TSC sync check time for core-siblings

For each logical CPU that is coming online, we spend 20msec for
checking the TSC synchronization. And as this is done
sequentially for each logical CPU boot, this time gets added up
depending on the number of logical CPU's supported by the
platform.

Minimize this by using the socket topology information.

If the target CPU coming online doesn't have any of its
core-siblings online, a timeout of 20msec will be used for the
TSC-warp measurement loop. Otherwise a smaller timeout of 2msec
will be used, as we have some information about this socket
already (and this information grows as we have more and more
logical-siblings in that socket).

Ideally we should be able to skip the TSC sync check on the
other core-siblings, if the first logical CPU in a socket passed
the sync test. But as the TSC is per-logical CPU and can
potentially be modified wrongly by the bios before the OS boot,
TSC sync test for smaller duration should be able to catch such
errors. Also this will catch the condition where all the cores
in the socket doesn't get reset at the same time.

For example, with this modification, time spent in TSC sync
checks on a 4 socket 10-core with HT system gets reduced from
1580msec to 212msec.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jack Steiner <steiner@sgi.com>
Cc: venki@google.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1328581940.29790.20.camel@sbsiddha-desk.sc.intel.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>