All modifications to the watchdog_inuse_map happen with d->watchdog_lock held,
so there are no concurrency problems to deal with.
Furthermore, there is no need to use a loop to locate the next available
watchdog. As the bitmap is currently 2 bits wide and is stored in a uint32_t,
the next available timer can be located in O(1) time using bit-scanning
instructions.
No change in behaviour, but should have less cache-coherency impact.
Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
---
CC: Jan Beulich <jbeul...@suse.com>
CC: Wei Liu <wei.l...@citrix.com>
CC: Roger Pau Monné <roger....@citrix.com>
CC: Stefano Stabellini <sstabell...@kernel.org>
CC: Julien Grall <julien.gr...@arm.com>
CC: George Dunlap <george.dun...@eu.citrix.com>
CC: Edwin Török <edvin.to...@citrix.com>
CC: Christian Lindig <christian.lin...@citrix.com>
CC: Pau Ruiz Safont <pau.saf...@citrix.com>
---
xen/common/schedule.c | 14 ++++++--------
1 file changed, 6 insertions(+), 8 deletions(-)
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 89aba88..98c2c35 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -1068,17 +1068,15 @@ static long domain_watchdog(struct domain *d, uint32_t
id, uint32_t timeout)
}
else /* Allocate the next available timer. */
{
- for ( id = 0; id < NR_DOMAIN_WATCHDOG_TIMERS; id++ )
- {
- if ( test_and_set_bit(id, &d->watchdog_inuse_map) )
- continue;
- break;
- }
- if ( id == NR_DOMAIN_WATCHDOG_TIMERS )
+ id = ffs(~d->watchdog_inuse_map) - 1;
+
+ if ( unlikely(id >= NR_DOMAIN_WATCHDOG_TIMERS) )
{
rc = -ENOSPC;
goto unlock;
}
+
+ __set_bit(id, &d->watchdog_inuse_map);
rc = id + 1;
}
@@ -1086,7 +1084,7 @@ static long domain_watchdog(struct domain *d, uint32_t
id, uint32_t timeout)
if ( unlikely(timeout == 0) )
{
stop_timer(&d->watchdog_timer[id]);
- clear_bit(id, &d->watchdog_inuse_map);
+ __clear_bit(id, &d->watchdog_inuse_map);
}
else
set_timer(&d->watchdog_timer[id], NOW() + SECONDS(timeout));
--
2.1.4
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