Re: sendto syscall is slow

[Martin Dalecki <dalecki@evision-ventures.com>]

Martin Devera wrote:
> 
> Hello,
> 
> i'm doing new qos discipline developement and use own
> mesurment tool. It simply uses PF_PACKET and then
> doing sendto/recv simulating various flows.
> (I use both lo and eth0 where I short-connected RX-TX
>  pins in single ethcard)
> 
> I can't get beyond 25 000 packets per second. gprof:
> Each sample counts as 0.01 seconds.
>   %   cumulative   self              self     total
>  time   seconds   seconds    calls  ms/call  ms/call  name
>  35.67      5.39     5.39   498750     0.01     0.01  sendto
>  26.67      9.42     4.03  1000826     0.00     0.00  poll
>  19.06     12.30     2.88   498750     0.01     0.01  recv
> 
> Is there any faster way to force raw packets to kernel ? I need
> to push qos discipline to its edge but I can't because send
> syscall is bottleneck.
> Is it possible to tx multiple packets in sinhle call or should
> I extend kernel myself for this testing purpose ?

Increase the HZ constant in the kernel, which is determining the
sceduler frequency, which is apparently due to BH handling acting
as a low-pass filder for your siganls here. However please
beware of
many possible sideffects this may have on your system.