netdev - [PATCH net-next 4/4] tuntap: Increase the number of queues in tun.

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Date:	Tue, 18 Nov 2014 21:52:58 +0530
From:	Pankaj Gupta <pagupta@...hat.com>
To:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Cc:	davem@...emloft.net, jasowang@...hat.com, mst@...hat.com,
	dgibson@...hat.com, vfalico@...il.com, edumazet@...gle.com,
	vyasevic@...hat.com, hkchu@...gle.com,
	wuzhy@...ux.vnet.ibm.com.pnq.redhat.com, xemul@...allels.com,
	therbert@...gle.com, bhutchings@...arflare.com, xii@...gle.com,
	stephen@...workplumber.org, jiri@...nulli.us,
	sergei.shtylyov@...entembedded.com,
	Pankaj Gupta <pagupta@...hat.com>
Subject: [PATCH net-next 4/4] tuntap: Increase the number of queues in tun.

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 patches:
        net: allow large number of rx queues
        tuntap: Reduce the size of tun_struct by using flex array
        tuntap: Accepts tuntap max queue length as net sysctl parameter

        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@...hat.com>
Reviewed-by: David Gibson <dgibson@...hat.com>
---
 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 a9b3eb4..2fb31b7 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -115,10 +115,11 @@ 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.
+ */
+#define MAX_TAP_QUEUES 256
 #define MIN_TAP_QUEUES 1
 #define MAX_TAP_FLOWS  4096
 
-- 
1.8.3.1

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