s390/qdio: clear DSCI early for polling drivers

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Polling drivers in a configuration with 1 Input Queue currently keep
their DSCI armed all the way through the poll cycle, until
qdio_start_irq() clears it.

_Any_ intermittent QDIO interrupt delivered to tiqdio_thinint_handler()
will thus cause
1) the 'adapter_int' statistic to be incremented,
2) a call to tiqdio_call_inq_handlers() for this device, and then
3) the 'int_discarded' statistics to be incremented.

This causes overhead & complexity in the IRQ path, along with ambiguity
in the statistics.
On the other hand the device should be in IRQ avoidance mode during a
poll cycle, so there won't be a lot of DSCI ping-pong that this
micro-optimization could prevent.

So align the DSCI handling with what we already do for devices with
multiple Input Queues: clear it right away while processing the IRQ.

For the non-polling path this means that we no longer need to handle
the 1-queue case separately.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

...

This commit is contained in:

Julian Wiedmann 2020-03-20 14:00:00 +01:00 • committed by Vasily Gorbik

parent a8a4ee2740

commit 9c159bbc14

3 changed files with 2 additions and 26 deletions

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1

drivers/s390/cio/qdio.h

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2

drivers/s390/cio/qdio_main.c

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25

drivers/s390/cio/qdio_thinint.c

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