Messages in this thread | | | Date | Wed, 15 Mar 2023 14:33:27 +0100 | From | 'Horatiu Vultur' <> | Subject | Re: [PATCH net-next 2/2] net: lan966x: Stop using packing library |
| |
The 03/13/2023 17:04, David Laight wrote: > > From: Horatiu Vultur > > Sent: 12 March 2023 20:24 > > > > When a frame is injected from CPU, it is required to create an IFH(Inter > > frame header) which sits in front of the frame that is transmitted. > > This IFH, contains different fields like destination port, to bypass the > > analyzer, priotity, etc. Lan966x it is using packing library to set and > > get the fields of this IFH. But this seems to be an expensive > > operations. > > If this is changed with a simpler implementation, the RX will be > > improved with ~5Mbit while on the TX is a much bigger improvement as it > > is required to set more fields. Below are the numbers for TX. > ... > > +static void lan966x_ifh_set(u8 *ifh, size_t val, size_t pos, size_t length) > > +{ > > + u32 v = 0; > > + > > + for (int i = 0; i < length ; i++) { > > + int j = pos + i; > > + int k = j % 8; > > + > > + if (i == 0 || k == 0) > > + v = ifh[IFH_LEN_BYTES - (j / 8) - 1]; > > + > > + if (val & (1 << i)) > > + v |= (1 << k); > > + > > + if (i == (length - 1) || k == 7) > > + ifh[IFH_LEN_BYTES - (j / 8) - 1] = v; > > + } > > +} > > + > > It has to be possible to do much better that that. > Given that 'pos' and 'length' are always constants it looks like > each call should reduce to (something like): > ifh[k] |= val << n; > ifk[k + 1] |= val >> (8 - n); > ... > It might be that the compiler manages to do this, but I doubt it.
Thanks for the review. I will update this in the next version.
Do you think it is worth updating the code in lan966x_ifh_get to use byte access and not to read each bit individually? As there is no much improvement on the RX side that is using lan966x_ifh_get.
> > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) >
-- /Horatiu
| |