Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Lee Revell <rlrevell@joe-job.com>]

On Thu, 2004-09-02 at 18:14, Ingo Molnar wrote:
> * Lee Revell <rlrevell@joe-job.com> wrote:
> 
> > > i've given up on the netdev_backlog_granularity approach, and as a
> > > replacement i've modified specific network drivers to return at a safe
> > > point if softirq preemption is requested.
> > 
> > Makes sense, netdev_max_backlog never made a difference on my system
> > (via-rhine driver).
> 
> via-rhine does RX processing from the hardirq handler, this codepath is
> harder to break up. The NAPI ->poll functions used by e100 and 8193too
> are much easier to break up because RX throttling and re-trying is a
> basic property of NAPI.
> 

Judging from these graphs, all of the latency issues are solved, at
least on my UP hardware, and the latencies seem to be getting very close
to the limits of what the hardware can do:

http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/jack-test-1

The worst case latency is only 160 usecs, and the vast majority fall
into the pattern from 0 to 120 usecs.  All of the spikes above 120 are
almost certainly caused by netdev_max_backlog.  However these are not
long enough to cause any problems with my workload; the lowest practical
latency for audio work is around 0.66 ms (32 frames at 48khz). 

Lee