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powerpc/xics: Reduce and comment xics IPI use of memory barriers 

A single full sync (mb()) is requrired to order the mmio to the qirr reg
with the set or clear of the message word.  However, test_and_clear_bit
has the effect of smp_mb() and we are not doing any other io from here,
so we don't need a mb per bit processed.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Milton Miller 2008-10-10 01:56:44 +00:00 committed by Benjamin Herrenschmidt
parent 2172fe8704
commit 199f45c45e
1 changed files with 1 additions and 4 deletions
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5
arch/powerpc/platforms/pseries/xics.c
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@ -498,26 +498,23 @@ static irqreturn_t xics_ipi_dispatch(int cpu)
{
WARN_ON(cpu_is_offline(cpu));
mb(); /* order mmio clearing qirr */
while (xics_ipi_message[cpu].value) {
if (test_and_clear_bit(PPC_MSG_CALL_FUNCTION,
&xics_ipi_message[cpu].value)) {
mb();
smp_message_recv(PPC_MSG_CALL_FUNCTION);
}
if (test_and_clear_bit(PPC_MSG_RESCHEDULE,
&xics_ipi_message[cpu].value)) {
mb();
smp_message_recv(PPC_MSG_RESCHEDULE);
}
if (test_and_clear_bit(PPC_MSG_CALL_FUNC_SINGLE,
&xics_ipi_message[cpu].value)) {
mb();
smp_message_recv(PPC_MSG_CALL_FUNC_SINGLE);
}
#if defined(CONFIG_DEBUGGER) || defined(CONFIG_KEXEC)
if (test_and_clear_bit(PPC_MSG_DEBUGGER_BREAK,
&xics_ipi_message[cpu].value)) {
mb();
smp_message_recv(PPC_MSG_DEBUGGER_BREAK);
}
#endif