[PATCH v4 0/2] x86, mwaitt: introduce AMD mwaitt support

[Huang Rui]

Hi,

This patch set introduces a new instruction support on AMD Carrizo (Family
15h, Model 60h-6fh). It adds mwaitx delay function with a configurable
timer.

Andy and Boris provide a suggestion which use mwaitx on delay method.

Some discussions of the background, please see:
http://marc.info/?l=linux-kernel&m=143202042530498&w=2
http://marc.info/?l=linux-kernel&m=143161327003541&w=2
http://marc.info/?l=linux-kernel&m=143222815331016&w=2

They are rebased on tip/master.

Changes from v1 -> v2
- Remove mwaitx idle implementation since some disputes without power
  improvement.
- Add a patch which implement another use case on delay.
- Introduce a kernel parameter (delay) to make delay method configurable.

Changes from v2 -> v3
- Add compared data on commit message
- Remove kernel parameter
- Add hint to avoid to access deep state in future
- Update mwaitx delay method as Petter's suggestion

Changes from v3 -> v4
- Put the description into comments

I already do some testing with mwaitx on udelay.

Test scenario:

glb_loops = usec_to_tsc(delay_usec)
rdtsc -> read TSC counters as start
mwaitx_delay(glb_loops)
rdtsc -> read TSC counters as end
diff = end - start

Compared the real TSC counts (diff), that means the loops of counter goes.
And glb_loops is the input value of the EBX, that is the expect loops which
user configures. Below is 10000 us of mwaitx delay, we could see about 1200
(diff - glb_loops) delayed with mwaitx.

[ 2369.008651] start=4401974718758, end=4401992576888, diff=17858130, glb_loops=17856939

Thanks,
Rui

Huang Rui (2):
  x86, mwaitt: add monitorx and mwaitx instruction
  x86, mwaitt: introduce mwaix delay with a configurable timer

 arch/x86/include/asm/cpufeature.h |  1 +
 arch/x86/include/asm/mwait.h      | 51 +++++++++++++++++++++++++++++++++++++++
 arch/x86/lib/delay.c              | 41 ++++++++++++++++++++++++++++++-
 3 files changed, 92 insertions(+), 1 deletion(-)

-- 
1.9.1

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