Re: [PATCH v3 net-next 2/2 tuntap: Increase the number of queues in tun.

On Wed, Dec 3, 2014 at 5:52 PM, Michael S. Tsirkin [off-list ref] 
wrote:

On Wed, Dec 03, 2014 at 12:49:37PM +0530, Pankaj Gupta wrote:

quoted

 Networking under kvm works best if we allocate a per-vCPU RX and TX
 queue in a virtual NIC. This requires a per-vCPU queue on the host 
side.
 
 It is now safe to increase the maximum number of queues.
 Preceding patche: 'net: allow large number of rx queues'

s/patche/patch/

quoted

 made sure this won't cause failures due to high order memory
 allocations. Increase it to 256: this is the max number of vCPUs
 KVM supports.
 
 Signed-off-by: Pankaj Gupta [off-list ref]
 Reviewed-by: David Gibson [off-list ref]

Hmm it's kind of nasty that each tun device is now using x16 memory.
Maybe we should look at using a flex array instead, and removing the
limitation altogether (e.g. make it INT_MAX)?

But this only happens when IFF_MULTIQUEUE were used.
And core has vmalloc() fallback.
So probably not a big issue?

quoted

 ---
  drivers/net/tun.c | 9 +++++----
  1 file changed, 5 insertions(+), 4 deletions(-)
 
 diff --git a/drivers/net/tun.c b/drivers/net/tun.c
 index e3fa65a..a19dc5f8 100644
 --- a/drivers/net/tun.c
 +++ b/drivers/net/tun.c
 @@ -113,10 +113,11 @@ struct tap_filter {
  	unsigned char	addr[FLT_EXACT_COUNT][ETH_ALEN];
  };
  
 -/* DEFAULT_MAX_NUM_RSS_QUEUES were chosen to let the rx/tx queues 
allocated for
 - * the netdevice to be fit in one page. So we can make sure the 
success of
 - * memory allocation. TODO: increase the limit. */
 -#define MAX_TAP_QUEUES DEFAULT_MAX_NUM_RSS_QUEUES
 +/* MAX_TAP_QUEUES 256 is chosen to allow rx/tx queues to be equal
 + * to max number of vCPUS in guest. Also, we are making sure here
 + * queue memory allocation do not fail.

It's not queue memory allocation anymore, is it?
I would say "
This also helps the tfiles field fit in 4K, so the whole tun
device only needs an order-1 allocation.
"

quoted

 + */
 +#define MAX_TAP_QUEUES 256
  #define MAX_TAP_FLOWS  4096
  
  #define TUN_FLOW_EXPIRE (3 * HZ)
 -- 
 1.8.3.1
 
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