On 8/10/2017 8:54 AM, Frederic Weisbecker wrote:
But perhaps I should add a new NO_HZ_FULL_BUT_HOUSEKEEPING option.
Otherwise we'll change the meaning of NO_HZ_FULL_ALL way too much, to the point
that its default behaviour will be the exact opposite of the current one: by 
every CPU is housekeeping, so NO_HZ_FULL_ALL would have no effect anymore if we
don't set housekeeping boot option.

Maybe a CONFIG_HOUSEKEEPING_BOOT_ONLY as a way to restrict housekeeping
by default to just the boot cpu.  In conjunction with NOHZ_FULL_ALL you would
then get the expected semantics.

Also I plan to add a housekeeping option to offload the residual 1Hz tick from
nohz_full CPUs. So having "housekeeping=0,tick_offload" would make CPU 0 the
housekeeper, make the other CPUs nohz_full and handle their 1hz tick from CPU 0.

It does seem like that might be implied by requesting NOHZ_FULL on the core...
or maybe it's just implied by TASK_ISOLATION.  I've done a bad job of finding 
to work on that since last year's Plumbers, but September looks good :)

Chris Metcalf, Mellanox Technologies

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