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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>
This commit is contained in:
Vineet Gupta 2016-02-19 07:57:41 +05:30
parent 9681787930
commit 3dea30ca5b
1 changed files with 10 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
arch/arc/kernel/mcip.c
View File

@ -40,26 +40,19 @@ static void mcip_ipi_send(int cpu)
return; return;
} }
raw_spin_lock_irqsave(&mcip_lock, flags);
/* /*
* NOTE: We must spin here if the other cpu hasn't yet * If receiver already has a pending interrupt, elide sending this one.
* serviced a previous message. This can burn lots * Linux cross core calling works well with concurrent IPIs
* of time, but we MUST follows this protocol or * coalesced into one
* ipi messages can be lost!!! * see arch/arc/kernel/smp.c: ipi_send_msg_one()
* 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.
*/ */
__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); raw_spin_unlock_irqrestore(&mcip_lock, flags);
#ifdef CONFIG_ARC_IPI_DBG #ifdef CONFIG_ARC_IPI_DBG