iwlwifi: use paged Rx

This switches the iwlwifi driver to use paged skb from linear skb for Rx
buffer. So that it relieves some Rx buffer allocation pressure for the
memory subsystem. Currently iwlwifi (4K for 3945) requests 8K bytes for
Rx buffer. Due to the trailing skb_shared_info in the skb->data,
alloc_skb() will do the next order allocation, which is 16K bytes. This
is suboptimal and more likely to fail when the system is under memory
usage pressure. Switching to paged Rx skb lets us allocate the RXB
directly by alloc_pages(), so that only order 1 allocation is required.

It also adjusts the area spin_lock (with IRQ disabled) protected in the
tasklet because tasklet guarentees to run only on one CPU and the new
unprotected code can be preempted by the IRQ handler. This saves us from
spawning another workqueue to make skb_linearize/__pskb_pull_tail happy
(which cannot be called in hard irq context).

Finally, mac80211 doesn't support paged Rx yet. So we linearize the skb
for all the management frames and software decryption or defragmentation
required data frames before handed to mac80211. For all the other frames,
we __pskb_pull_tail 64 bytes in the linear area of the skb for mac80211
to handle them properly.

Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/drivers/net/wireless/iwlwifi/iwl-commands.h b/drivers/net/wireless/iwlwifi/iwl-commands.h
index cc4e9122709e..7d4f131708f3 100644
--- a/drivers/net/wireless/iwlwifi/iwl-commands.h
+++ b/drivers/net/wireless/iwlwifi/iwl-commands.h
@@ -3544,6 +3544,16 @@ struct iwl_wimax_coex_cmd {
  *****************************************************************************/
 
 struct iwl_rx_packet {
+	/*
+	 * The first 4 bytes of the RX frame header contain both the RX frame
+	 * size and some flags.
+	 * Bit fields:
+	 * 31:    flag flush RB request
+	 * 30:    flag ignore TC (terminal counter) request
+	 * 29:    flag fast IRQ request
+	 * 28-14: Reserved
+	 * 13-00: RX frame size
+	 */
 	__le32 len_n_flags;
 	struct iwl_cmd_header hdr;
 	union {