linux-kernel - [PATCH v5 net-next 2/2] tuntap: Increase the number of queues in tun.

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Message-Id: <1421043089-30103-3-git-send-email-pagupta@redhat.com>
Date:	Mon, 12 Jan 2015 11:41:29 +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,
	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 v5 net-next 2/2] 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 patch: 'net: allow large number of rx queues'
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.

Size of tun_struct changes from 8512 to 10496 after this patch. This keeps
pages allocated for tun_struct before and after the patch to 3.

Signed-off-by: Pankaj Gupta <pagupta@...hat.com>
Reviewed-by: David Gibson <dgibson@...hat.com>
---
 drivers/net/tun.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index e3fa65a..a3f13f7 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -113,10 +113,9 @@ 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. */
+#define MAX_TAP_QUEUES 256
 #define MAX_TAP_FLOWS  4096
 
 #define TUN_FLOW_EXPIRE (3 * HZ)
-- 
1.8.3.1

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