diff options
| author | Vineet Gupta <vgupta@synopsys.com> | 2016-02-19 07:57:41 +0530 |
|---|---|---|
| committer | Vineet Gupta <vgupta@synopsys.com> | 2016-02-24 11:07:31 +0530 |
| commit | 3dea30ca5bef0e013abe857057a952a9d6757fe5 (patch) | |
| tree | c0bf423e97bc81fc881d97c772dd8454ae622e87 /arch/arc | |
| parent | 9681787930cec7cee77db0a93c747153ef962b8a (diff) | |
| download | linux-3dea30ca5bef0e013abe857057a952a9d6757fe5.tar.bz2 | |
ARCv2: Elide sending new cross core intr if receiver didn't ack prev
ARConnect/MCIP IPI sending has a retry-wait loop in case caller had
not seen a previous such interrupt. Turns out that it is not needed at
all. Linux cross core calling allows coalescing multiple IPIs to same
receiver - it is fine as long as there is one.
This logic is built into upper layer already, at a higher level of
abstraction. ipi_send_msg_one() sets the actual msg payload, but it only
calls MCIP IPI sending if msg holder was empty (using
atomic-set-new-and-get-old construct). Thus it is unlikely that the
retry-wait looping was ever getting exercised at all.
Cc: Chuck Jordan <cjordan@synopsys.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Diffstat (limited to 'arch/arc')
| -rw-r--r-- | arch/arc/kernel/mcip.c | 27 |
1 files changed, 10 insertions, 17 deletions
diff --git a/arch/arc/kernel/mcip.c b/arch/arc/kernel/mcip.c index e30d5d428330..7afc3c703ed1 100644 --- a/arch/arc/kernel/mcip.c +++ b/arch/arc/kernel/mcip.c @@ -40,26 +40,19 @@ static void mcip_ipi_send(int cpu) return; } + raw_spin_lock_irqsave(&mcip_lock, flags); + /* - * NOTE: We must spin here if the other cpu hasn't yet - * serviced a previous message. This can burn lots - * of time, but we MUST follows this protocol or - * ipi messages can be lost!!! - * Also, we must release the lock in this loop because - * the other side may get to this same loop and not - * be able to ack -- thus causing deadlock. + * If receiver already has a pending interrupt, elide sending this one. + * Linux cross core calling works well with concurrent IPIs + * coalesced into one + * see arch/arc/kernel/smp.c: ipi_send_msg_one() */ + __mcip_cmd(CMD_INTRPT_READ_STATUS, cpu); + ipi_was_pending = read_aux_reg(ARC_REG_MCIP_READBACK); + if (!ipi_was_pending) + __mcip_cmd(CMD_INTRPT_GENERATE_IRQ, cpu); - do { - raw_spin_lock_irqsave(&mcip_lock, flags); - __mcip_cmd(CMD_INTRPT_READ_STATUS, cpu); - ipi_was_pending = read_aux_reg(ARC_REG_MCIP_READBACK); - if (ipi_was_pending == 0) - break; /* break out but keep lock */ - raw_spin_unlock_irqrestore(&mcip_lock, flags); - } while (1); - - __mcip_cmd(CMD_INTRPT_GENERATE_IRQ, cpu); raw_spin_unlock_irqrestore(&mcip_lock, flags); #ifdef CONFIG_ARC_IPI_DBG |