On 09/15/2014 11:39 AM, Peter Hurley wrote:
> On 09/15/2014 10:00 AM, Frans Klaver wrote:
>> At 3.6Mbaud, with slightly over 2Mbit/s data coming in, we see 1600 uart
>> rx buffer overflows within 30 seconds. Threading the interrupt handling reduces
>> this to about 170 overflows in 10 minutes.
>
> Why is the threadirqs kernel boot option not sufficient?
> Or conversely, shouldn't this be selectable?
Also, do you see the same performance differential when you implement this
in the 8250 driver (that is, on top of Sebastian's omap->8250 conversion)?
> Regards,
> Peter Hurley
>
> PS - To overflow the 64 byte RX FIFO at those data rates means interrupt
> latency in excess of 250us?
>
>> In practice this therefore reduces the need for hardware flow control,
>> meaning the sending side doesn't have to buffer as much either.
>>
>> Signed-off-by: Frans Klaver <frans.klaver@xxxxxxxxx>
>> ---
>> drivers/tty/serial/omap-serial.c | 30 +++++++++++++++++++++++-------
>> 1 file changed, 23 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
>> index 7d3f557..398139a 100644
>> --- a/drivers/tty/serial/omap-serial.c
>> +++ b/drivers/tty/serial/omap-serial.c
>> @@ -575,6 +575,20 @@ static void serial_omap_rdi(struct uart_omap_port *up, unsigned int lsr)
>> }
>>
>> /**
>> + * serial_omap_fast_irq() - schedule interrupt handling
>> + */
>> +static irqreturn_t serial_omap_fast_irq(int irq, void *dev_id)
>> +{
>> + struct uart_omap_port *up = dev_id;
>> + unsigned int iir = serial_in(up, UART_IIR);
>> +
>> + if (iir & UART_IIR_NO_INT)
>> + return IRQ_NONE;
>> +
>> + return IRQ_WAKE_THREAD;
>> +}
>> +
>> +/**
>> * serial_omap_irq() - This handles the interrupt from one port
>> * @irq: uart port irq number
>> * @dev_id: uart port info
>> @@ -584,7 +598,6 @@ static irqreturn_t serial_omap_irq(int irq, void *dev_id)
>> struct uart_omap_port *up = dev_id;
>> unsigned int iir, lsr;
>> unsigned int type;
>> - irqreturn_t ret = IRQ_NONE;
>> int max_count = 256;
>>
>> spin_lock(&up->port.lock);
>> @@ -595,7 +608,6 @@ static irqreturn_t serial_omap_irq(int irq, void *dev_id)
>> if (iir & UART_IIR_NO_INT)
>> break;
>>
>> - ret = IRQ_HANDLED;
>> lsr = serial_in(up, UART_LSR);
>>
>> /* extract IRQ type from IIR register */
>> @@ -634,7 +646,7 @@ static irqreturn_t serial_omap_irq(int irq, void *dev_id)
>> pm_runtime_put_autosuspend(up->dev);
>> up->port_activity = jiffies;
>>
>> - return ret;
>> + return IRQ_HANDLED;
>> }
>>
>> static unsigned int serial_omap_tx_empty(struct uart_port *port)
>> @@ -731,15 +743,19 @@ static int serial_omap_startup(struct uart_port *port)
>> /*
>> * Allocate the IRQ
>> */
>> - retval = request_irq(up->port.irq, serial_omap_irq, up->port.irqflags,
>> - up->name, up);
>> + retval = request_threaded_irq(up->port.irq, serial_omap_fast_irq,
>> + serial_omap_irq,
>> + IRQF_ONESHOT | up->port.irqflags,
>> + up->name, up);
>> if (retval)
>> return retval;
>>
>> /* Optional wake-up IRQ */
>> if (up->wakeirq) {
>> - retval = request_irq(up->wakeirq, serial_omap_irq,
>> - up->port.irqflags, up->name, up);
>> + retval = request_threaded_irq(up->wakeirq, serial_omap_fast_irq,
>> + serial_omap_irq,
>> + IRQF_ONESHOT | up->port.irqflags,
>> + up->name, up);
>> if (retval) {
>> free_irq(up->port.irq, up);
>> return retval;
>>
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