From: Michael Neuling Date: Tue, 8 Jun 2010 04:57:02 +0000 (+1000) Subject: powerpc: Enable asymmetric SMT scheduling on POWER7 X-Git-Tag: v2.6.36-rc1~531^2~18 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=76cbd8a8f8b0dddbff89a6708bd5bd13c0d21a00;p=pandora-kernel.git powerpc: Enable asymmetric SMT scheduling on POWER7 The POWER7 core has dynamic SMT mode switching which is controlled by the hypervisor. There are 3 SMT modes: SMT1 uses thread 0 SMT2 uses threads 0 & 1 SMT4 uses threads 0, 1, 2 & 3 When in any particular SMT mode, all threads have the same performance as each other (ie. at any moment in time, all threads perform the same). The SMT mode switching works such that when linux has threads 2 & 3 idle and 0 & 1 active, it will cede (H_CEDE hypercall) threads 2 and 3 in the idle loop and the hypervisor will automatically switch to SMT2 for that core (independent of other cores). The opposite is not true, so if threads 0 & 1 are idle and 2 & 3 are active, we will stay in SMT4 mode. Similarly if thread 0 is active and threads 1, 2 & 3 are idle, we'll go into SMT1 mode. If we can get the core into a lower SMT mode (SMT1 is best), the threads will perform better (since they share less core resources). Hence when we have idle threads, we want them to be the higher ones. This adds a feature bit for asymmetric packing to powerpc and then enables it on POWER7. Signed-off-by: Michael Neuling Signed-off-by: Peter Zijlstra Acked-by: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: linuxppc-dev@ozlabs.org LKML-Reference: <20100608045702.31FB5CC8C7@localhost.localdomain> Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed