Commit 52f4f918 authored Sep 30, 2015 by Arnd Bergmann Committed by David S. Miller Oct 05, 2015

mwifiex: avoid gettimeofday in ba_threshold setting



mwifiex_get_random_ba_threshold() uses a complex homegrown implementation
to generate a pseudo-random number from the current time as returned
from do_gettimeofday().

This currently requires two 32-bit divisions plus a couple of other
computations that are eventually discarded as only eight bits of
the microsecond portion are used at all.

We could replace this with a call to get_random_bytes(), but that
might drain the entropy pool too fast if this is called for each
packet.

Instead, this patch converts it to use ktime_get_ns(), which is a
bit faster than do_gettimeofday(), and then uses a similar algorithm
as before, but in a way that takes both the nanosecond and second
portion into account for slightly-more-but-still-not-very-random
pseudorandom number.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Amitkumar Karwar <akarwar@marvell.com>
Cc: Nishant Sarmukadam <nishants@marvell.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: linux-wireless@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>

parent e253fb74

drivers/net/wireless/mwifiex/wmm.c

+4 −11

Original line number	Diff line number	Diff line
		@@ -117,22 +117,15 @@ mwifiex_wmm_allocate_ralist_node(struct mwifiex_adapter adapter, const u8 ra)
		*/
		static u8 mwifiex_get_random_ba_threshold(void)
		{
		u32 sec, usec;
		struct timeval ba_tstamp;
		u8 ba_threshold;

		u64 ns;
		/* setup ba_packet_threshold here random number between
		* [BA_SETUP_PACKET_OFFSET,
		* BA_SETUP_PACKET_OFFSET+BA_SETUP_MAX_PACKET_THRESHOLD-1]
		*/
		ns = ktime_get_ns();
		ns += (ns >> 32) + (ns >> 16);

		do_gettimeofday(&ba_tstamp);
		sec = (ba_tstamp.tv_sec & 0xFFFF) + (ba_tstamp.tv_sec >> 16);
		usec = (ba_tstamp.tv_usec & 0xFFFF) + (ba_tstamp.tv_usec >> 16);
		ba_threshold = (((sec << 16) + usec) % BA_SETUP_MAX_PACKET_THRESHOLD)
		+ BA_SETUP_PACKET_OFFSET;

		return ba_threshold;
		return ((u8)ns % BA_SETUP_MAX_PACKET_THRESHOLD) + BA_SETUP_PACKET_OFFSET;
		}

		/*

Admin message