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

[Jason Wang]

On Wed, Dec 3, 2014 at 5:52 PM, Michael S. Tsirkin <mst@xxxxxxxxxx> 
wrote:
> On Wed, Dec 03, 2014 at 12:49:37PM +0530, Pankaj Gupta wrote:
> >  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/
>
> >  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 <pagupta@xxxxxxxxxx>
> >  Reviewed-by: David Gibson <dgibson@xxxxxxxxxx>
>
> 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?

> >  ---
> >   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.
> "
>
> >  + */
> >  +#define MAX_TAP_QUEUES 256
> >   #define MAX_TAP_FLOWS  4096
> >   
> >   #define TUN_FLOW_EXPIRE (3 * HZ)
> >  -- 
> >  1.8.3.1
> >  
> >  --
> >  To unsubscribe from this list: send the line "unsubscribe netdev" in
> >  the body of a message to majordomo@xxxxxxxxxxxxxxx
> >  More majordomo info at  http://vger.kernel.org/majordomo-info.html

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/