Messages in this thread | | | Subject | Re: Long latencies with MD RAID 1 [was Re: libata/sata_nv latency on NVIDIA CK804 ] | From | Lee Revell <> | Date | Wed, 15 Mar 2006 19:48:47 -0500 |
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On Wed, 2006-03-15 at 19:21 -0500, Bill Rugolsky Jr. wrote: > On Wed, Mar 15, 2006 at 06:44:02PM -0500, Lee Revell wrote: > > On Wed, 2006-03-15 at 18:14 -0500, Bill Rugolsky Jr. wrote: > > > [Meanwhile, I still have to switch contexts and look at the long > > > softirq latencies that at first glance appear to be due to the use of > > > mempool by the RAID1 bio code.] > > > > Can you post traces of them somewhere? There are no long running > > softirqs in the two you posted (the worst is only 200 usecs or so). > > This is typical of what I'm seeing. It seems to be looping over lots > of io request completions? > > -Bill > > preemption latency trace v1.1.5 on 2.6.16-rc6-git4-latency > -------------------------------------------------------------------- > latency: 1950 us, #8586/8586, CPU#0 | (M:desktop VP:0, KP:0, SP:0 HP:0 #P:1)
This looks very similar to what I see with my regular ATA drive (except that the completions are handled in hardirq context).
You can cause less work to be done in each softirq by lowering /sys/block/$DEV/queue/max_sectors_kb.
I would not consider ~2ms "long", there are some other softirqs that induce 10-15ms latencies...
Lee
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