On Thu, 2014-08-21 at 15:04 -0700, Benjamin Poirier wrote: > On 2014/08/19 15:00, Michael Chan wrote: > > On Tue, 2014-08-19 at 11:52 -0700, Benjamin Poirier wrote: > > > diff --git a/drivers/net/ethernet/broadcom/tg3.c > > > b/drivers/net/ethernet/broadcom/tg3.c > > > index 3ac5d23..b11c0fd 100644 > > > --- a/drivers/net/ethernet/broadcom/tg3.c > > > +++ b/drivers/net/ethernet/broadcom/tg3.c > > > @@ -202,7 +202,8 @@ static inline void _tg3_flag_clear(enum TG3_FLAGS > > > flag, unsigned long *bits) > > > #endif > > > > > > /* minimum number of free TX descriptors required to wake up TX process > > > */ > > > -#define TG3_TX_WAKEUP_THRESH(tnapi) ((tnapi)->tx_pending / 4) > > > +#define TG3_TX_WAKEUP_THRESH(tnapi) max_t(u32, (tnapi)->tx_pending / > > > 4, \ > > > + MAX_SKB_FRAGS + 1) > > > > I think we should precompute this and store it in something like > > tp->tx_wake_thresh. > > I've tried this by adding the following patch at the end of the v2 > series but I did not measure a significant latency improvement. Was > there another reason for the change?
Just performance. The wake up threshold is checked in the tx fast path in both start_xmit() and tg3_tx(). I would optimize such code for speed as much as possible. In the current code, it was just a right shift operation. Now, with max_t() added, I think I prefer having it pre-computed. The performance difference may not be measurable, but I think the compiled code size may be smaller too. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
