Messages in this thread | | | Date | Thu, 4 Dec 2014 12:20:13 +0200 | From | "Michael S. Tsirkin" <> | Subject | Re: [PATCH v3 net-next 2/2 tuntap: Increase the number of queues in tun. |
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On Thu, Dec 04, 2014 at 03:03:34AM +0008, Jason Wang wrote: > > > On Wed, Dec 3, 2014 at 5:52 PM, Michael S. Tsirkin <mst@redhat.com> 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@redhat.com> > >> Reviewed-by: David Gibson <dgibson@redhat.com> > > > >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.
I refer to this field: struct tun_file __rcu *tfiles[MAX_TAP_QUEUES]; if we make MAX_TAP_QUEUES 256, this will use 4K bytes, apparently unconditionally.
> 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@vger.kernel.org > >> More majordomo info at http://vger.kernel.org/majordomo-info.html
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