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

K.R. Foley
2004-08-25T14:35:42Z

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