Re: [RFC] ATH9K: infinite loop in Tasklet

[Felix Fietkau <nbd@openwrt.org>]

On 2013-01-02 9:13 PM, Adrian Chadd wrote:
> On 2 January 2013 09:15, voncken <cedric.voncken@acksys.fr> wrote:
>>         Yes,
>>
>>         I used an mpc8314 at 400Mhz, with 128 Mbit of RAM for my test.
> 
> Ah!
> 
>>         To find it, I measured the time elapsing in ath_rxbuf_alloc(..) with
>> the kernel function local_clock().
>>
>>         With SLOB I found around 123 us (and I have an infinite loop in
>> ath9k tasklet, because when I have consumed one packet the next packet is
>> ready to rx process)
>>         With SLAB I found around 22 us
>>         With SLUB I found around 10 us
> 
> Cool. That's significantly more CPU.. :-)
> 
> So yes, the right thing to do here is to break out after a limit is
> reached, and if we hit that limit, re-schedule that tasklet to run.
I don't think it's worth adding such a band-aid. NAPI handles this much
better, as the network stack specifies a limit for the number of frames
to be accepted and doesn't poll if it doesn't have room for more, thus
solving this in a much better way.

- Felix