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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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
drivers/s390/cio/qdio.h
View File

@ -374,7 +374,6 @@ int tiqdio_allocate_memory(void);
void tiqdio_free_memory(void);
int tiqdio_register_thinints(void);
void tiqdio_unregister_thinints(void);
void clear_nonshared_ind(struct qdio_irq *);
int test_nonshared_ind(struct qdio_irq *);
/* prototypes for setup */

2
drivers/s390/cio/qdio_main.c
View File

@ -1643,8 +1643,6 @@ int qdio_start_irq(struct ccw_device *cdev)
if (!irq_ptr)
return -ENODEV;
clear_nonshared_ind(irq_ptr);
for_each_input_queue(irq_ptr, q, i)
qdio_stop_polling(q);

25
drivers/s390/cio/qdio_thinint.c
View File

@ -82,32 +82,16 @@ void tiqdio_remove_device(struct qdio_irq *irq_ptr)
INIT_LIST_HEAD(&irq_ptr->entry);
}
static inline int has_multiple_inq_on_dsci(struct qdio_irq *irq_ptr)
{
return irq_ptr->nr_input_qs > 1;
}
static inline int references_shared_dsci(struct qdio_irq *irq_ptr)
{
return irq_ptr->dsci == &q_indicators[TIQDIO_SHARED_IND].ind;
}
void clear_nonshared_ind(struct qdio_irq *irq_ptr)
{
if (!is_thinint_irq(irq_ptr))
return;
if (references_shared_dsci(irq_ptr) ||
has_multiple_inq_on_dsci(irq_ptr))
return;
xchg(irq_ptr->dsci, 0);
}
int test_nonshared_ind(struct qdio_irq *irq_ptr)
{
if (!is_thinint_irq(irq_ptr))
return 0;
if (references_shared_dsci(irq_ptr) ||
has_multiple_inq_on_dsci(irq_ptr))
if (references_shared_dsci(irq_ptr))
return 0;
if (*irq_ptr->dsci)
return 1;
@ -127,8 +111,7 @@ static inline void tiqdio_call_inq_handlers(struct qdio_irq *irq)
struct qdio_q *q;
int i;
if (!references_shared_dsci(irq) &&
has_multiple_inq_on_dsci(irq))
if (!references_shared_dsci(irq))
xchg(irq->dsci, 0);
if (irq->irq_poll) {
@ -140,10 +123,6 @@ static inline void tiqdio_call_inq_handlers(struct qdio_irq *irq)
return;
}
if (!references_shared_dsci(irq) &&
!has_multiple_inq_on_dsci(irq))
xchg(irq->dsci, 0);
for_each_input_queue(irq, q, i) {
/*
* Call inbound processing but not directly