Hi Arnd, > From: Arnd Bergmann [mailto:arnd@xxxxxxxx] > Sent: Wednesday, September 30, 2015 4:57 PM > To: netdev@xxxxxxxxxxxxxxx > Cc: y2038@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; David S. > Miller; Arnd Bergmann; Amitkumar Karwar; Nishant Sarmukadam; Kalle Valo; > linux-wireless@xxxxxxxxxxxxxxx > 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@xxxxxxxx> > Cc: Amitkumar Karwar <akarwar@xxxxxxxxxxx> > Cc: Nishant Sarmukadam <nishants@xxxxxxxxxxx> > Cc: Kalle Valo <kvalo@xxxxxxxxxxxxxx> > Cc: linux-wireless@xxxxxxxxxxxxxxx > --- > 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@xxxxxxxxxxx> Regards, Amitkumar -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
