On 03/26/2013 08:29 PM, Jan Kiszka wrote:
On 2013-03-26 20:17, Jan Kiszka wrote:
Hi Philippe,
I'm trying to understand how the new Linux-to-RT migration process works
under forge and specifically I-pipe core. It currently looks to me like
we are delaying this needlessly:
- __ipipe_migrate_head() suspends the calling Linux thread and triggers
a context switch
- after the switch, __ipipe_switch_tail and then
complete_domain_migration is invoked
- complete_domain_migration stalls head and calls ipipe_migration_hook.
We are still running over the root domain.
- ipipe_migration_hook in forge wakes up the RT thread and calls
xnpod_schedule
- as we are in root, xnarch_escalate triggers and calls ipipe_raise_irq
- as the head domain is stalled, dispatch_irq_head just marks the
escalation VIRQ pending, not handler is called, no actual RT
rescheduling can be performed on its return
- we eventually return to complete_domain_migration and simply clear
the stall flag. No pending IRQs are process, again no VIRQ is
delivered
- only when we receive the next IRQ or have some other reason for
checking the head domain's IRQ log, the pending VIRQ will finally be
processed
Did I miss something or should we actually perform some
__ipipe_sync_stage in complete_domain_migration to accelerate the switch?
Or rather this:
diff --git a/kernel/ipipe/core.c b/kernel/ipipe/core.c
index 53e82ef..d164b4c 100644
--- a/kernel/ipipe/core.c
+++ b/kernel/ipipe/core.c
@@ -1102,6 +1102,7 @@ static void complete_domain_migration(void) /* hw IRQs
off */
__set_bit(IPIPE_STALL_FLAG, &p->status);
ipipe_migration_hook(t);
__clear_bit(IPIPE_STALL_FLAG, &p->status);
+ __ipipe_do_sync_pipeline(p->domain);
}
#endif /* !CONFIG_IPIPE_LEGACY */
Nitpicking: in theory, the code should expect the migration hook to have
actually done the work, and not delayed it like Xenomai currently does
in practice. A safer check would be as follows, allowing further
arch-dependent handling in case the migration did succeed (typically for
Blackfin):
diff --git a/kernel/ipipe/core.c b/kernel/ipipe/core.c
index 96b3a98..c4598ad 100644
--- a/kernel/ipipe/core.c
+++ b/kernel/ipipe/core.c
@@ -1102,6 +1102,8 @@ static void complete_domain_migration(void) /* hw
IRQs off */
__set_bit(IPIPE_STALL_FLAG, &p->status);
ipipe_migration_hook(t);
__clear_bit(IPIPE_STALL_FLAG, &p->status);
+ if (__ipipe_ipending_p(p))
+ __ipipe_sync_pipeline(p->domain);
}
#endif /* !CONFIG_IPIPE_LEGACY */
--
Philippe.
_______________________________________________
Xenomai mailing list
[email protected]
http://www.xenomai.org/mailman/listinfo/xenomai
