I've noticed less responsive disk response on 2.4.0 vs. 2.2.17. For example --
I run vmware and suspend it frequently when I'm not using it. One of them requires
a 158Mb save file. Before, I could suspend that one, then start another which
reads in a smaller 50M save file. The smaller one would come up while the other
was still saving. As of 2.4, the smaller one doesn't come up -- I can't even do
an 'ls' until the big save finishes.
Now big image program has actually exited and I can close the window -- the disk
writes are going on from the disk cache with 'kupdate' taking some minor fraction (<1%)
of the CPU and the rest of the system being mostly idle.
If I have vmstat running, I notice blocks trickling out to the disk, 5sec averages
495,142,151,155,136,257,15,0. Note that the maximum read rate (hdparm -t) of this
disk is in the 12-14M/s range. I'm getting about 1-5% of that on output with the
system's disk subsystem being apparently unable to do anything else.
This is with IDE hard disk with DMA enabled.
a) is this expected performance on a large linear write?
b) should I expect other disk operations to be denied service as long as
the write is 'flushing'?
-l
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