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SubjectRe: [RFC PATCH] virtio-net: reset virtqueue affinity when doing cpu hotplug
On 12/27/2012 11:28 AM, Jason Wang wrote:
> On 12/26/2012 06:19 PM, Wanlong Gao wrote:
>> On 12/26/2012 06:06 PM, Jason Wang wrote:
>>> On 12/26/2012 03:06 PM, Wanlong Gao wrote:
>>>> Add a cpu notifier to virtio-net, so that we can reset the
>>>> virtqueue affinity if the cpu hotplug happens. It improve
>>>> the performance through enabling or disabling the virtqueue
>>>> affinity after doing cpu hotplug.
>>> Hi Wanlong:
>>>
>>> Thanks for looking at this.
>>>> Cc: Rusty Russell <rusty@rustcorp.com.au>
>>>> Cc: "Michael S. Tsirkin" <mst@redhat.com>
>>>> Cc: Jason Wang <jasowang@redhat.com>
>>>> Cc: virtualization@lists.linux-foundation.org
>>>> Cc: netdev@vger.kernel.org
>>>> Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
>>>> ---
>>>> drivers/net/virtio_net.c | 39 ++++++++++++++++++++++++++++++++++++++-
>>>> 1 file changed, 38 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>>> index a6fcf15..9710cf4 100644
>>>> --- a/drivers/net/virtio_net.c
>>>> +++ b/drivers/net/virtio_net.c
>>>> @@ -26,6 +26,7 @@
>>>> #include <linux/scatterlist.h>
>>>> #include <linux/if_vlan.h>
>>>> #include <linux/slab.h>
>>>> +#include <linux/cpu.h>
>>>>
>>>> static int napi_weight = 128;
>>>> module_param(napi_weight, int, 0444);
>>>> @@ -34,6 +35,8 @@ static bool csum = true, gso = true;
>>>> module_param(csum, bool, 0444);
>>>> module_param(gso, bool, 0444);
>>>>
>>>> +static bool cpu_hotplug = false;
>>>> +
>>>> /* FIXME: MTU in config. */
>>>> #define MAX_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
>>>> #define GOOD_COPY_LEN 128
>>>> @@ -1041,6 +1044,26 @@ static void virtnet_set_affinity(struct virtnet_info *vi, bool set)
>>>> vi->affinity_hint_set = false;
>>>> }
>>>>
>>>> +static int virtnet_cpu_callback(struct notifier_block *nfb,
>>>> + unsigned long action, void *hcpu)
>>>> +{
>>>> + switch(action) {
>>>> + case CPU_ONLINE:
>>>> + case CPU_ONLINE_FROZEN:
>>>> + case CPU_DEAD:
>>>> + case CPU_DEAD_FROZEN:
>>>> + cpu_hotplug = true;
>>>> + break;
>>>> + default:
>>>> + break;
>>>> + }
>>>> + return NOTIFY_OK;
>>>> +}
>>>> +
>>>> +static struct notifier_block virtnet_cpu_notifier = {
>>>> + .notifier_call = virtnet_cpu_callback,
>>>> +};
>>>> +
>>>> static void virtnet_get_ringparam(struct net_device *dev,
>>>> struct ethtool_ringparam *ring)
>>>> {
>>>> @@ -1131,7 +1154,14 @@ static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
>>>> */
>>>> static u16 virtnet_select_queue(struct net_device *dev, struct sk_buff *skb)
>>>> {
>>>> - int txq = skb_rx_queue_recorded(skb) ? skb_get_rx_queue(skb) :
>>>> + int txq;
>>>> +
>>>> + if (unlikely(cpu_hotplug == true)) {
>>>> + virtnet_set_affinity(netdev_priv(dev), true);
>>>> + cpu_hotplug = false;
>>>> + }
>>>> +
>>> Why don't you just do this in callback?
>> Callback can just give us a "hcpu", can't get the virtnet_info from callback. Am I missing something?
>
> Well, I think you can just embed the notifier block into virtnet_info,
> then use something like container_of in the callback to make the
> notifier per device. This also solve the concern of Eric.

Yeah, thank you very much for your suggestion. I'll try it.

>>> btw. Does qemu/kvm support cpu-hotplug now?
>> From http://www.linux-kvm.org/page/CPUHotPlug, I saw that qemu-kvm can support hotplug
>> but failed to merge to qemu.git, right?
>
> Not sure, I just try latest qemu, it even does not have a cpu_set command.

Adding Igor to CC,

As I know, hotplug support is cleaned from qemu, and Igor want to rework it but not been completed?
I'm not sure about that, Igor, could you send out your tech-preview-patches?

Thanks,
Wanlong Gao

>
> Thanks
>>
>> Thanks,
>> Wanlong Gao
>>
>
>



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