s390/cpum_sf: load program parameter at sampler enablement

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The lpp instruction is used to place the PID of the current
task in the program-parameter (PP) register.  The register
contents is then included in the sampling data entries.

The lpp instruction loads the PP register only when at least
one sampling function is enabled.  Otherwise it is executed
as a no-op.

Linux calls lpp at context switch.  If the context switch
happens before the sampler is enabled, the PP register is
empty.  That means, the PID of the task that is sampled is
not stored in sampling data until the next context switch.

Hence, always call lpp when enabling the sampler.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

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Hendrik Brueckner 2017-10-27 15:45:19 +02:00 • committed by Martin Schwidefsky

parent de9954b75e

commit d4c7e649d7

2 changed files with 9 additions and 0 deletions

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6

arch/s390/include/asm/cpu_mf.h

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3

arch/s390/kernel/perf_cpum_sf.c

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