Hi again,
On 09.02.2015 14:33, Kaspar Schleiser wrote:
Hi Joakim,
On 02/09/15 14:20, Joakim Gebart wrote:
Has anyone measured the cost of the thread context switching on the
different platforms? I'm mainly interested in Cortex-M4 (Kinetis). This
would be a good indication of how "slow" an I/O device has to be before
it is worth it to manually yield a thread while waiting.
AFAIR, Hauke measured the context switch cost from msg_send in one
thread to msg_receive in another with around 500 instructions on
Cortex-M3. A wakeup (one thread running, IRQ triggered saving that
context, ISR triggers wakeup of another thread) will probably be a
litte less than half of that.
the it was ~550 cycles for sending a message from thread to another, to
for msg_send(), context_save, running scheduler, context_restore (of
receiving thread), and msg_receive().
Putting a thread to sleep (so switchting to the idle thread) and waking
it up again would need 2 context switches -> ~1000 cycles...
Cheers,
Hauke
Consider these figures not very precise. ;)
Kaspar
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