From 52f4f91893955c359885d022b2142e2326f020a1 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Wed, 30 Sep 2015 13:26:35 +0200 Subject: [PATCH] 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 Cc: Amitkumar Karwar Cc: Nishant Sarmukadam Cc: Kalle Valo Cc: linux-wireless@vger.kernel.org Signed-off-by: David S. Miller --- drivers/net/wireless/mwifiex/wmm.c | 15 ++++----------- 1 file changed, 4 insertions(+), 11 deletions(-) diff --git a/drivers/net/wireless/mwifiex/wmm.c b/drivers/net/wireless/mwifiex/wmm.c index 173d3663c2e0..878d358063dc 100644 --- a/drivers/net/wireless/mwifiex/wmm.c +++ b/drivers/net/wireless/mwifiex/wmm.c @@ -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; } /* -- 2.20.1