Subject: Re: [PATCH net-next 2/4] sfc: allocate rx pages on the same node as the interrupt

From: "Daniel Pieczko (dpieczko)" <[email-masked]>
Date: Mon, 2 Nov 2015 13:17:22 +0000

On 28/10/15 15:59, Eric Dumazet wrote:
> On Wed, 2015-10-28 at 15:01 +0000, Shradha Shah wrote:
>> From: Daniel Pieczko <[email-masked]>
>>
>> When the interrupt servicing a channel is on a NUMA node that is
>> not local to the device, performance is improved by allocating
>> rx pages on the node local to the interrupt (remote to the device)
>>
>> The performance-optimal case, where interrupts and applications
>> are pinned to CPUs on the same node as the device, is not altered
>> by this change.
>>
>> This change gave a 1% improvement in transaction rate using Nginx
>> with all interrupts and Nginx threads on the node remote to the
>> device. It also gave a small reduction in round-trip latency,
>> again with the interrupt and application on a different node to
>> the device.
>>
>> Allocating rx pages based on the channel->irq_node value is only
>> valid for the initial driver-load interrupt affinities; if an
>> interrupt is moved later, the wrong node may be used for the
>> allocation.
>>
>> Signed-off-by: Shradha Shah <[email-masked]>
>> ---
>>  drivers/net/ethernet/sfc/efx.c        |  1 +
>>  drivers/net/ethernet/sfc/net_driver.h |  3 +++
>>  drivers/net/ethernet/sfc/rx.c         | 14 +++++++++-----
>>  3 files changed, 13 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c
>> index 974637d..89fbd03 100644
>> --- a/drivers/net/ethernet/sfc/efx.c
>> +++ b/drivers/net/ethernet/sfc/efx.c
>> @@ -445,6 +445,7 @@ efx_alloc_channel(struct efx_nic *efx, int i, struct efx_channel *old_channel)
>>  	channel->efx = efx;
>>  	channel->channel = i;
>>  	channel->type = &efx_default_channel_type;
>> +	channel->irq_node = NUMA_NO_NODE;
>>  
>>  	for (j = 0; j < EFX_TXQ_TYPES; j++) {
>>  		tx_queue = &channel->tx_queue[j];
>> diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
>> index ad56231..0ab9080a 100644
>> --- a/drivers/net/ethernet/sfc/net_driver.h
>> +++ b/drivers/net/ethernet/sfc/net_driver.h
>> @@ -419,6 +419,7 @@ enum efx_sync_events_state {
>>   * @sync_events_state: Current state of sync events on this channel
>>   * @sync_timestamp_major: Major part of the last ptp sync event
>>   * @sync_timestamp_minor: Minor part of the last ptp sync event
>> + * @irq_node: NUMA node of interrupt
>>   */
>>  struct efx_channel {
>>  	struct efx_nic *efx;
>> @@ -477,6 +478,8 @@ struct efx_channel {
>>  	enum efx_sync_events_state sync_events_state;
>>  	u32 sync_timestamp_major;
>>  	u32 sync_timestamp_minor;
>> +
>> +	int irq_node;
>>  };
>>  
>>  #ifdef CONFIG_NET_RX_BUSY_POLL
>> diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
>> index 3f0e129..c5ef1e8 100644
>> --- a/drivers/net/ethernet/sfc/rx.c
>> +++ b/drivers/net/ethernet/sfc/rx.c
>> @@ -168,11 +168,15 @@ static int efx_init_rx_buffers(struct efx_rx_queue *rx_queue, bool atomic)
>>  			 * context in such a case.  So, use __GFP_NO_WARN
>>  			 * in case of atomic.
>>  			 */
>> -			page = alloc_pages(__GFP_COLD | __GFP_COMP |
>> -					   (atomic ?
>> -					    (GFP_ATOMIC | __GFP_NOWARN)
>> -					    : GFP_KERNEL),
>> -					   efx->rx_buffer_order);
>> +			struct efx_channel *channel;
>> +
>> +			channel = efx_rx_queue_channel(rx_queue);
>> +			page = alloc_pages_node(channel->irq_node, __GFP_COMP |
>> +						(atomic ?
>> +						 (GFP_ATOMIC | __GFP_NOWARN)
>> +						 : GFP_KERNEL),
>> +						efx->rx_buffer_order);
>> +
>>  			if (unlikely(page == NULL))
>>  				return -ENOMEM;
>>  			dma_addr =
>>
>
> Sorry, I do not understand this patch, and why the following one is not
> squashed on this one.
>
> irq_node is always NUMA_NO_NODE (in this patch)
>
> So you claim a 1% improvement, switching from alloc_pages(...) to
> alloc_pages_node(NUMA_NO_NODE, ...) ???
>

You're correct that this doesn't make sense as it is.  There is something missing in this patch (channel->irq_node should be set) and also changing the order of some patches could make this clearer.  The series will need to be resent.

Daniel