OpenE2K
/
linux
6
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

powerpc: Use bytes instead of bitops in smp ipi multiplexing 

Since there are only 4 messages, we can replace the atomic bit set
(which uses atomic load reserve and store conditional sequence) with
a byte stores to seperate bytes.  We still have to perform a load
reserve and store conditional sequence to avoid loosing messages on
reception but we can do that with a single call to xchg.

The do {} while and __BIG_ENDIAN specific mask testing was chosen by
looking at the generated asm code.  On gcc-4.4, the bit masking becomes
a simple bit mask and test of the register returned from xchg without
storing and loading the value to the stack like attempts with a union
of bytes and an int (or worse, loading single bit constants from the
constant pool into non-voliatle registers that had to be preseved on
the stack).  The do {} while avoids an unconditional branch to the
end of the loop to test the entry / repeat condition of a while loop
and instead optimises for the expected single iteration of the loop.

We have a full mb() at the beginning to cover ordering between send,
ipi, and receive so we can use xchg_local and forgo the further
acquire and release barriers of xchg.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Milton Miller 2011-05-10 19:29:46 +00:00 committed by Benjamin Herrenschmidt
parent 1ece355b68
commit 714542721b
1 changed files with 18 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
arch/powerpc/kernel/smp.c
View File

@ -180,7 +180,7 @@ int smp_request_message_ipi(int virq, int msg)
#ifdef CONFIG_PPC_SMP_MUXED_IPI
struct cpu_messages {
unsigned long messages; /* current messages bits */
int messages; /* current messages */
unsigned long data; /* data for cause ipi */
};
static DEFINE_PER_CPU_SHARED_ALIGNED(struct cpu_messages, ipi_message);
@ -195,9 +195,9 @@ void smp_muxed_ipi_set_data(int cpu, unsigned long data)
void smp_muxed_ipi_message_pass(int cpu, int msg)
{
struct cpu_messages *info = &per_cpu(ipi_message, cpu);
unsigned long *tgt = &info->messages;
char *message = (char *)&info->messages;
set_bit(msg, tgt);
message[msg] = 1;
mb();
smp_ops->cause_ipi(cpu, info->data);
}
@ -205,30 +205,35 @@ void smp_muxed_ipi_message_pass(int cpu, int msg)
void smp_muxed_ipi_resend(void)
{
struct cpu_messages *info = &__get_cpu_var(ipi_message);
unsigned long *tgt = &info->messages;
if (*tgt)
if (info->messages)
smp_ops->cause_ipi(smp_processor_id(), info->data);
}
irqreturn_t smp_ipi_demux(void)
{
struct cpu_messages *info = &__get_cpu_var(ipi_message);
unsigned long *tgt = &info->messages;
unsigned int all;
mb(); /* order any irq clear */
while (*tgt) {
if (test_and_clear_bit(PPC_MSG_CALL_FUNCTION, tgt))
do {
all = xchg_local(&info->messages, 0);
#ifdef __BIG_ENDIAN
if (all & (1 << (24 - 8 * PPC_MSG_CALL_FUNCTION)))
generic_smp_call_function_interrupt();
if (test_and_clear_bit(PPC_MSG_RESCHEDULE, tgt))
if (all & (1 << (24 - 8 * PPC_MSG_RESCHEDULE)))
reschedule_action(0, NULL); /* upcoming sched hook */
if (test_and_clear_bit(PPC_MSG_CALL_FUNC_SINGLE, tgt))
if (all & (1 << (24 - 8 * PPC_MSG_CALL_FUNC_SINGLE)))
generic_smp_call_function_single_interrupt();
#if defined(CONFIG_DEBUGGER) || defined(CONFIG_KEXEC)
if (test_and_clear_bit(PPC_MSG_DEBUGGER_BREAK, tgt))
if (all & (1 << (24 - 8 * PPC_MSG_DEBUGGER_BREAK)))
debug_ipi_action(0, NULL);
#else
#error Unsupported ENDIAN
#endif
}
} while (info->messages);
return IRQ_HANDLED;
}
#endif /* CONFIG_PPC_SMP_MUXED_IPI */