linux-kernel - Re: [RFC 1/4] net: allow large number of rx queues

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Message-ID: <53F23B4C.2000507@cogentembedded.com>
Date:	Mon, 18 Aug 2014 21:43:40 +0400
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Pankaj Gupta <pagupta@...hat.com>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
CC:	davem@...emloft.net, jasowang@...hat.com, mst@...hat.com,
	dgibson@...hat.com, vfalico@...il.com, edumazet@...gle.com,
	vyasevic@...hat.com, hkchu@...gle.com, wuzhy@...ux.vnet.ibm.com,
	xemul@...allels.com, therbert@...gle.com,
	bhutchings@...arflare.com, xii@...gle.com,
	stephen@...workplumber.org
Subject: Re: [RFC 1/4] net: allow large number of rx queues

Hello.

On 08/18/2014 05:37 PM, Pankaj Gupta wrote:

> netif_alloc_rx_queues() uses kcalloc() to allocate memory
> for "struct netdev_queue *_rx" array.
> If we are doing large rx queue allocation kcalloc() might
> fail, so this patch does a fallback to vzalloc().
> Similar implementation is done for tx queue allocation in
> netif_alloc_netdev_queues().

> We avoid failure of high order memory allocation
> with the help of vzalloc(), this allows us to do large
> rx and tx queue allocation which in turn helps us to
> increase the number of queues in tun.

> As vmalloc() adds overhead on a critical network path,
> __GFP_REPEAT flag is used with kzalloc() to do this fallback
> only when really needed.

> Signed-off-by: Pankaj Gupta <pagupta@...hat.com>
> Reviewed-by: Michael S. Tsirkin <mst@...hat.com>
> Reviewed-by: David Gibson <dgibson@...hat.com>
> ---
>   net/core/dev.c | 20 +++++++++++++-------
>   1 file changed, 13 insertions(+), 7 deletions(-)

> diff --git a/net/core/dev.c b/net/core/dev.c
> index 1c15b18..a455a02 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -5942,17 +5942,24 @@ void netif_stacked_transfer_operstate(const struct net_device *rootdev,
>   EXPORT_SYMBOL(netif_stacked_transfer_operstate);
>
>   #ifdef CONFIG_SYSFS
> +static void netif_free_rx_queues(struct net_device *dev)
> +{
> +	kvfree(dev->_rx);
> +}
> +
>   static int netif_alloc_rx_queues(struct net_device *dev)
>   {
>   	unsigned int i, count = dev->num_rx_queues;
>   	struct netdev_rx_queue *rx;
> -
> +	size_t sz = count * sizeof(*rx);

   Please keep an empty line after declarations.

>   	BUG_ON(count < 1);
>

WBR, Sergei

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