Messages in this thread | | | From | Pankaj Gupta <> | Subject | [RFC 0/4] Increase the limit of tuntap queues | Date | Mon, 18 Aug 2014 19:07:16 +0530 |
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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. Modern physical NICs have multiqueue support for large number of queues. To scale vNIC to run multiple queues parallel to maximum number of vCPU's we need to increase number of queues support in tuntap.
This series is to increase the limit of tuntap queues. Original work is being done by 'jasowang@redhat.com'. I am taking this 'https://lkml.org/lkml/2013/6/19/29' patch series as a reference. As per discussion in the patch series:
There were two reasons which prevented us from increasing number of tun queues:
- The netdev_queue array in netdevice were allocated through kmalloc, which may cause a high order memory allocation too when we have several queues. E.g. sizeof(netdev_queue) is 320, which means a high order allocation would happens when the device has more than 16 queues.
- We store the hash buckets in tun_struct which results a very large size of tun_struct, this high order memory allocation fail easily when the memory is fragmented.
The patch 60877a32bce00041528576e6b8df5abe9251fa73 increases the number of tx queues. Memory allocation fallback to vzalloc() when kmalloc() fails.
This series tries to address following issues:
- Increase the number of netdev_queue queues for rx similarly its done for tx queues by falling back to vzalloc() when memory allocation with kmalloc() fails.
- Switches to use flex array to implement the flow caches to avoid higher order allocations.
- Publish maximum number of queues as read only module_param so that user space application like libvirt can use this value to limit number of queues. Also Administrators can specify number of queues at module load time.
- Increase number of queues to 256, maximum number is equal to maximum number of vCPUS allowed in a guest.
I have done some testing to find out any regression and with sample program which creates tun/tap for single queue / multiqueue device and it seems to be working fine.
tuntap: Increase the number of queues in tun tuntap: Reduce the size of tun_struct by using flex array tuntap: Publish tuntap max queue length as module_param net: allow large number of rx queues
drivers/net/tun.c | 71 ++++++++++++++++++++++++++++++++++++++++-------------- net/core/dev.c | 20 +++++++++------ 2 files changed, 66 insertions(+), 25 deletions(-)
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