lkml.org 
[lkml]   [2015]   [Sep]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 05/12] mwifiex: avoid gettimeofday in ba_threshold setting
    Date
    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;
    }

    /*
    --
    2.1.0.rc2


    \
     
     \ /
      Last update: 2015-09-30 14:01    [W:4.150 / U:0.128 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site