Messages in this thread | | | Subject | Re: [PATCH net-next v1 5/6] tg3: implementation of a non-NAPI mode | From | Eric Dumazet <> | Date | Fri, 16 Dec 2011 20:50:42 +0100 |
| |
Le vendredi 16 décembre 2011 à 10:19 -0800, David Decotigny a écrit : > From: Tom Herbert <therbert@google.com> > > The tg3 NIC has a hard limit of 511 descriptors for the receive ring. > Under heavy load of small packets, this device receive queue may not > be serviced fast enough to prevent packets drops. This could be due > to a variety of reasons such as lengthy processing delays of packets > in the stack, softirqs being disabled too long, etc. If the driver is > run in non-NAPI mode, the RX queue is serviced in the device > interrupt, which is much less likely to be deferred for a substantial > period of time. > > There are some effects in not using NAPI that need to be considered. > It does increase the chance of live-lock in interrupt handler, > although since the tg3 does interrupt coalescing this is very unlikely > to occur. Also, more code is being run with interrupts disabled > potentially deferring other hardware interrupts. The amount of time > spent in the interrupt handler should be minimized by dequeuing > packets of the device queue and queuing them to a host queue as > quickly as possible. > > The default mode of operation remains NAPI and its performances are > kept unchanged (code unchanged). Non-NAPI mode is enabled by > commenting-out CONFIG_TIGON3_NAPI Kconfig parameter. > >
Oh well, thats ugly :(
I suspect this was only used with RPS/RFS ?
Or interrupts stick on a given cpu ?
Because with a default setup, and IRQ serviced by multiple cpus, you endup with possible packet reorderings.
Packet1,2,3,4 handled by CPU0 : queued on netif_rx() queue. EndOfInterrupt Packet4,5,6,7 handled by CPU1 : queued on netif_rx() queue. EndOfInterrupt
CPU0/CPU1 happily merge packets...
-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |