Re: [patch] voluntary-preempt-2.6.8.1-P9

[K.R. Foley]

Lee Revell wrote:
> On Tue, 2004-08-24 at 23:17, K.R. Foley wrote:
>
> > Ingo Molnar wrote:
> >
> > >  http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.8.1-P9
>
>
> > latency trace of ~148 usec in scsi_request? I don't know if this is real 
> > or not. Note the 79 usec here:
> >
> > 00000001 0.107ms (+0.079ms): sd_init_command (scsi_prep_fn)
> >
> > Entire trace is here:
> >
> > http://www.cybsft.com/testresults/2.6.8.1-P9/latency_trace7.txt
> >
> >
> > Is this possible? This is not the first time I have seen this. There is 
> > another one here:
> >
> > http://www.cybsft.com/testresults/2.6.8.1-P9/latency_trace5.txt
>
>
> This looks like a real latency.  What is
> /sys/block/sdX/queue/max_sectors_kb set to?  Does lowering it help?
>
> Lee
/sys/block/sda/queue/max_sectors_kb was set to 512, trying it at 256. 
Hard to say whether it is helping or not. Looking at dmesg I do see some 
traces for scsi_request in the range of 39 - 72 usec. However, anything 
higher (up to 115 usec) could be masked by one of the netif_skb 
latencies that I am still seeing. Not only that, but I have only caught 
a hand-full of these scsi traces in all of my testing.

kr
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