netdev - Re: [PATCH net-next] sfc: allocate rx pages on the same node as the interrupt

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Date:	Tue, 10 May 2016 07:55:06 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Edward Cree <ecree@...arflare.com>
Cc:	linux-net-drivers@...arflare.com,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Daniel Pieczko <dpieczko@...arflare.com>
Subject: Re: [PATCH net-next] sfc: allocate rx pages on the same node as the
 interrupt

On Tue, 2016-05-10 at 15:21 +0100, Edward Cree wrote:
> From: Daniel Pieczko <dpieczko@...arflare.com>
> 
> 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.

Yes, I advocated for such changes in the past for mlx4 NIC.

But your patch makes no sense to me.

alloc_pages() by default would run on the cpu servicing the IRQ, so
would automatically provide pages on the local node.

If you care only of the initial pages allocated with GFP_KERNEL at
device start, really that is a small detail as they should be consumed
and replaced quite fast.

If you worry that "wrong" pages would be reused over and over,
you could make sure that efx_reuse_page() wont reuse a page on the wrong
node.

page_to_nid(page) != numa_mem_id() 

Note that this could happen even if IRQ are not changed since
alloc_pages() could in stress situations give you a page from a remote
node.