Adam Kropelin wrote:
>
> ..
> dd if=/dev/hda1 of=/dev/null bs=1M
>
> ...in parallel with...
>
> dd if=/dev/zero of=/mnt/foo bs=1M
>
> When you kick in the write load, the read throughput drops to < 1
> MB/sec. `vmstat 1` output below shows the transition...
>
> --Adam
>
> procs memory swap io system cpu
> r b w swpd free buff cache si so bi bo in cs us sy id
> 2 0 0 4272 112684 20356 36856 0 0 0 16 1016 72 5 0 95
> 0 1 1 4272 108476 23676 36856 0 0 3320 0 1067 224 13 4 83
> 1 0 1 4272 96656 35580 36856 0 0 11904 0 1192 474 30 39 30
> 0 1 0 4272 84836 47356 36856 0 0 11776 0 1192 463 30 42 27
> 0 1 1 4272 72956 59268 36856 0 0 11904 40 1313 1139 44 38 18
> 0 1 0 4272 61076 71044 36856 0 0 11776 0 1200 478 29 43 29
> 0 1 0 4272 49256 82828 36856 0 0 11784 0 1199 522 39 37 24
> 0 1 0 4272 37196 94732 36856 0 0 11904 0 1199 497 35 38 26
> 0 1 0 4272 25256 106508 36856 0 0 11776 0 1199 512 32 43 24
> 1 2 3 4692 2468 75604 90132 0 420 9608 10888 1189 721 19 75 6
> 0 2 3 4692 3540 46932 117580 0 0 808 10428 1093 287 30 70 0
> 0 2 3 4692 3448 42916 121624 0 0 1024 8824 1099 266 65 35 0
> 0 2 3 4692 3200 35152 129692 0 0 1024 6512 1088 294 55 45 0
> 0 2 4 4692 1564 24640 141696 0 0 768 7688 1091 277 44 56 0
> 1 1 2 4692 3492 19044 145484 0 0 1024 5956 1084 285 69 31 0
Your bandwidth there fell from 12 megs/sec to around 8. That is
reasonable, I think. It's just that the read-vs-write balance is
wrong for you.
Try changing drivers/block/deadline-iosched.c:fifo_batch to 16.
And the application isn't performing enough caching, perhaps.
The VM could be fairly easily changed to defer writeback if there is
read activity happening on the same spindle. Been thinking about
that (and its relative, early flush) a bit. But that write has
to go to disk sometime.
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This archive was generated by hypermail 2b29 : Thu Nov 07 2002 - 22:00:50 EST