Subject: Re: [PATCH net-next V2 5/5] net/mlx4_en: Add a service task

From: Amir Vadai <[email-masked]>
Date: Tue, 23 Apr 2013 16:56:43 +0300

On 22/04/2013 22:01, Eric Dumazet wrote:
> On Mon, 2013-04-22 at 14:56 +0300, Amir Vadai wrote:
>> Add a service task to run tasks that needed to be executed periodically.
>> Currently the only task is a watchdog to catch NIC clock overflow, to make
>> timestamping accurate.
>> Will move the statistics task into this framework in a later patch.
>>
>> Signed-off-by: Amir Vadai <[email-masked]>
>> ---
>>  drivers/net/ethernet/mellanox/mlx4/en_clock.c  |   20 ++++++++++++++++++++
>>  drivers/net/ethernet/mellanox/mlx4/en_netdev.c |   24 ++++++++++++++++++++++++
>>  drivers/net/ethernet/mellanox/mlx4/mlx4_en.h   |    4 ++++
>>  3 files changed, 48 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_clock.c b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
>> index 6d8227d..c1982a4 100644
>> --- a/drivers/net/ethernet/mellanox/mlx4/en_clock.c
>> +++ b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
>> @@ -126,4 +126,24 @@ void mlx4_en_init_timestamp(struct mlx4_en_dev *mdev)
>>  
>>  	timecounter_init(&mdev->clock, &mdev->cycles,
>>  			 ktime_to_ns(ktime_get_real()));
>> +
>> +	/* Calculate period in seconds to call the overflow watchdog. Doing
>> +	 * that, by dividing the maximal cycles value in nano-seconds, convert
>> +	 * it to seconds, and divide by 2 - to make sure counter is checked at
>> +	 * least once every wrap around.
>> +	 */
>> +	mdev->overflow_period =
>> +		cyclecounter_cyc2ns(&mdev->cycles,
>> +				    mdev->cycles.mask) / 1000000 / 2;
>> +}
>> +
> 
> So this 1000000 looks like NSEC_PER_SEC/HZ ?
No. It is just a typo - used 10^6 instead of 10^9 for nano's.
But it is a good idea to have the HZ multiplied in the initialization of
overflow_period - will fix the calculation and change overflow_period
units to be jiffies, and not seconds.
> What if HZ=100 ?

Thanks,
Amir