you go into linux/include/blkdev.h and increase MAX_QUEUE_SECTORS to (2
<< (20 - 9)) and see if it makes any differences here? if it doesn't
make differences it could be the a bit increased readhaead but I doubt
it's the latter.
> ctar_load:
> Kernel [runs] Time CPU% Loads LCPU% Ratio
> 2.4.18 [3] 117.4 63 1 7 1.60
> 2.4.19 [2] 106.5 70 1 8 1.45
> 2.4.20-rc1 [3] 102.1 72 1 7 1.39
> 2.4.20-rc1aa1 [3] 107.1 69 1 7 1.46
> 2420rc2aa1 [1] 103.3 73 1 8 1.41
>
> xtar_load:
> Kernel [runs] Time CPU% Loads LCPU% Ratio
> 2.4.18 [3] 150.8 49 2 8 2.06
> 2.4.19 [1] 132.4 55 2 9 1.81
> 2.4.20-rc1 [3] 180.7 40 3 8 2.47
> 2.4.20-rc1aa1 [3] 166.6 44 2 7 2.28*
> 2420rc2aa1 [1] 217.7 34 4 9 2.97*
>
> Takes longer. Is only one run though so may not be an accurate average.
This most probably is a too small waitqueue. Of course increasing the
waitqueue will increase a bit the latency too for the other workloads,
it's a tradeoff and there's no way around it. Even read-latency has the
tradeoff when it chooses the "nth" place to be the seventh slot, where
to put the read request if it fails inserction.
>
>
> io_load:
> Kernel [runs] Time CPU% Loads LCPU% Ratio
> 2.4.18 [3] 474.1 15 36 10 6.48
> 2.4.19 [3] 492.6 14 38 10 6.73
> 2.4.20-rc1 [2] 1142.2 6 90 10 15.60
> 2.4.20-rc1aa1 [1] 1132.5 6 90 10 15.47
> 2420rc2aa1 [1] 164.3 44 10 9 2.24
>
> This was where the effect of the disk latency hack was expected to have an
> effect. It sure did.
yes, I certainly can feel the machine much more responsive during the
write load too. Too bad some benchmark like dbench decreased
significantly but I don't see too many ways around it. At least now with
those changes the contigous write case is unaffected, my storage test
box still reads and writes at over 100mbyte/sec for example, this
clearly means what matters is that we have 512k dma commands, not an
huge size of the queue. Really with a loaded machine and potential
scheduling delays it could matter more to have a larger queue, that
maybe why the performance is decreased for some workload here too, not
only because of a less effective elevator. So probably 2Mbyte of queue
is a much better idea, so at least we can have a ring with 4 elements to refill
after a completion wakeup, I wanted to be strict to see the "lowlatency" effect
at most in the first place. We could also consider to use a /4 instead of my
current /2 for the batch_sectors initialization.
BTW, at first glance it looks 2.5 has the same problem in the queue
sizing too.
> read_load:
> Kernel [runs] Time CPU% Loads LCPU% Ratio
> 2.4.18 [3] 102.3 70 6 3 1.40
> 2.4.19 [2] 134.1 54 14 5 1.83
> 2.4.20-rc1 [3] 173.2 43 20 5 2.37
> 2.4.20-rc1aa1 [3] 150.6 51 16 5 2.06
> 2420rc2aa1 [1] 140.5 51 13 4 1.92
>
> list_load:
> Kernel [runs] Time CPU% Loads LCPU% Ratio
> 2.4.18 [3] 90.2 76 1 17 1.23
> 2.4.19 [1] 89.8 77 1 20 1.23
> 2.4.20-rc1 [3] 88.8 77 0 12 1.21
> 2.4.20-rc1aa1 [1] 88.1 78 1 16 1.20
> 2420rc2aa1 [1] 99.7 69 1 19 1.36
>
> mem_load:
> Kernel [runs] Time CPU% Loads LCPU% Ratio
> 2.4.18 [3] 103.3 70 32 3 1.41
> 2.4.19 [3] 100.0 72 33 3 1.37
> 2.4.20-rc1 [3] 105.9 69 32 2 1.45
>
> Mem load hung the machine. I could not get rc2aa1 through this part of the
> benchmark no matter how many times I tried to run it. No idea what was going
> on. Easy to reproduce. Simply run the mem_load out of contest (which runs
> until it is killed) and the machine will hang.
sorry but what is mem_load supposed to do other than to loop forever? It
is running for two days on my test box (512m of ram, 2G of swap, 4-way
smp) and nothing happened yet. It's an infinite loop. Sounds like you're
trapping a signal. Wouldn't it be simpler to just finish after a number
of passes? The machine is perfectly usable and responsive during the
mem_load, xmms doesn't skip a beat for istance, this is probably thanks
to the elevator-lowlatency too, I recall xmms wasn't used to be
completely smooth during heavy swapping in previous kernels (because the read()
of the sound file didn't return in rasonable time since I'm swapping in the
same hd where I store the data).
jupiter:~ # uptime
4:20pm up 1 day, 14:43, 3 users, load average: 1.38, 1.28, 1.21
jupiter:~ # vmstat 1
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
0 1 0 197408 4504 112 1436 21 34 23 34 36 19 0 2 97
0 1 0 199984 4768 116 1116 11712 5796 11720 5804 514 851 1 2 97
0 1 0 234684 4280 108 1116 14344 12356 14344 12360 617 1034 0 3 96
0 1 0 267880 4312 108 1116 10464 11916 10464 11916 539 790 0 3 97
1 0 0 268704 5192 108 1116 6220 9336 6220 9336 363 474 0 1 99
0 1 0 270764 5312 108 1116 13036 18952 13036 18952 584 958 0 1 99
0 1 0 271368 5088 108 1116 8288 5160 8288 5160 386 576 0 1 99
0 1 1 269184 4296 108 1116 4352 6420 4352 6416 254 314 0 0 100
0 1 0 266528 4604 108 1116 9644 4652 9644 4656 428 658 0 1 99
there is no way I can reproduce any stability problem with mem_load here
(tested both on scsi quad xeon and ide dualathlon). Can you provide more
details of your problem and/or a SYSRQ+T during the hang? thanks.
Andrea
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/