Hi Arnd,
From: Arnd Bergmann [mailto:arnd@arndb.de] Sent: Wednesday, September 30, 2015 4:57 PM To: netdev@vger.kernel.org Cc: y2038@lists.linaro.org; linux-kernel@vger.kernel.org; David S. Miller; Arnd Bergmann; Amitkumar Karwar; Nishant Sarmukadam; Kalle Valo; linux-wireless@vger.kernel.org Subject: [PATCH 05/12] 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
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; }
/*
Looks fine to me. Acked-by: Amitkumar Karwar akarwar@marvell.com
Regards, Amitkumar