[PATCH v5 0/2] x86, mwaitt: introduce AMD mwaitt support

From: Huang Rui
Date: Mon Jun 15 2015 - 06:49:29 EST


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 MONITORX/MWAITX description into comments

Changes from v4 -> v5
- Remove mwaitx function
- Use mwaitx_delay at init_amd
- Use cpu_tts as montioring address scope

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/delay.h | 1 +
arch/x86/include/asm/mwait.h | 43 +++++++++++++++++++++++++++++++++++++
arch/x86/kernel/cpu/amd.c | 4 ++++
arch/x86/lib/delay.c | 45 +++++++++++++++++++++++++++++++++++++++
5 files changed, 94 insertions(+)

--
1.9.1

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