Re: [PATCH] cfq-iosched: reduce write depth only if sync was delayed

From: Jeff Moyer
Date: Fri Dec 18 2009 - 10:32:22 EST

Corrado Zoccolo <czoccolo@xxxxxxxxx> writes:

> Hi Jeff,
> On Wed, Dec 9, 2009 at 7:09 PM, Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:
>> Corrado Zoccolo <czoccolo@xxxxxxxxx> writes:
>>
>>> The numbers look good. Now, there is no penalty in having low_latency
>>> set for sequential writes, and just a small penalty for random ones.
>>> The fact that random reads are faster with low_latency set is interesting.
>>> Is the test is running with your patched tiobench (so that the number
>>> of random operations is comparable with sequential ones)?
>>
>> No, I forgot all about that. ÂThe number of random operations defaults
>> to 4000, which is pretty low. ÂI'll re-run the tests with a number
>> comparable to the sequential runs. ÂSorry about that.
>>
> N.P.
> if you have time, can you also re-run the test changing:
> iosched/fifo_expire_async to 8 ?
> I hope that reducing the expire_async, will make cfq quicker at switching
> between the different threads, allowing more parallelism for seq
> writers on your hw.
> If this is the case, I think I can try to estimate the
> fifo_expire_async in the autotuning patch.

Sorry this took so long. I've been rather busy of late.

Cheers,
Jeff

low_latency=1, fifo_expire_async=8

Unit information
================
File size = megabytes
Blk Size = bytes
Rate = megabytes per second
CPU% = percentage of CPU used during the test
Latency = milliseconds
Lat% = percent of requests that took longer than X seconds
CPU Eff = Rate divided by CPU% - throughput per cpu load

Sequential Reads
File Blk Num Avg Maximum Lat% Lat% CPU
Identifier Size Size Thr Rate (CPU%) Latency Latency >2s >10s Eff
---------------------------- ------ ----- --- ------ ------ --------- ----------- -------- -------- -----
2.6.32 8192 65536 8 88.39 89.74% 16.388 2032.62 0.00000 0.00000 98
2.6.32 8192 65536 16 90.77 185.3% 32.213 2175.99 0.00000 0.00000 49

Random Reads
File Blk Num Avg Maximum Lat% Lat% CPU
Identifier Size Size Thr Rate (CPU%) Latency Latency >2s >10s Eff
---------------------------- ------ ----- --- ------ ------ --------- ----------- -------- -------- -----
2.6.32 8192 65536 8 19.62 25.74% 71.827 3397.26 0.00000 0.00000 76
2.6.32 8192 65536 16 23.82 55.01% 103.361 4075.53 0.00000 0.00000 43

Sequential Writes
File Blk Num Avg Maximum Lat% Lat% CPU
Identifier Size Size Thr Rate (CPU%) Latency Latency >2s >10s Eff
---------------------------- ------ ----- --- ------ ------ --------- ----------- -------- -------- -----
2.6.32 8192 65536 8 108.28 1007.% 12.984 5643.55 0.00076 0.00000 11
2.6.32 8192 65536 16 112.40 2014.% 25.430 8592.98 0.00839 0.00000 6

Random Writes
File Blk Num Avg Maximum Lat% Lat% CPU
Identifier Size Size Thr Rate (CPU%) Latency Latency >2s >10s Eff
---------------------------- ------ ----- --- ------ ------ --------- ----------- -------- -------- -----
2.6.32 8192 65536 8 63.94 337.7% 22.885 6047.22 0.00076 0.00000 19
2.6.32 8192 65536 16 61.94 662.5% 46.997 12759.69 0.15411 0.00000 9


low_latency=0, fifo_expire_async=8

Unit information
================
File size = megabytes
Blk Size = bytes
Rate = megabytes per second
CPU% = percentage of CPU used during the test
Latency = milliseconds
Lat% = percent of requests that took longer than X seconds
CPU Eff = Rate divided by CPU% - throughput per cpu load

Sequential Reads
File Blk Num Avg Maximum Lat% Lat% CPU
Identifier Size Size Thr Rate (CPU%) Latency Latency >2s >10s Eff
---------------------------- ------ ----- --- ------ ------ --------- ----------- -------- -------- -----
2.6.32 8192 65536 8 89.13 88.30% 15.872 3101.39 0.00000 0.00000 101
2.6.32 8192 65536 16 86.78 161.7% 30.794 4909.02 0.00000 0.00000 54

Random Reads
File Blk Num Avg Maximum Lat% Lat% CPU
Identifier Size Size Thr Rate (CPU%) Latency Latency >2s >10s Eff
---------------------------- ------ ----- --- ------ ------ --------- ----------- -------- -------- -----
2.6.32 8192 65536 8 20.21 26.64% 69.863 4285.42 0.00000 0.00000 76
2.6.32 8192 65536 16 20.10 52.75% 139.761 5986.94 0.00076 0.00000 38

Sequential Writes
File Blk Num Avg Maximum Lat% Lat% CPU
Identifier Size Size Thr Rate (CPU%) Latency Latency >2s >10s Eff
---------------------------- ------ ----- --- ------ ------ --------- ----------- -------- -------- -----
2.6.32 8192 65536 8 108.74 1020.% 13.070 5331.78 0.00076 0.00000 11
2.6.32 8192 65536 16 112.18 2020.% 25.559 7903.16 0.00992 0.00000 6

Random Writes
File Blk Num Avg Maximum Lat% Lat% CPU
Identifier Size Size Thr Rate (CPU%) Latency Latency >2s >10s Eff
---------------------------- ------ ----- --- ------ ------ --------- ----------- -------- -------- -----
2.6.32 8192 65536 8 64.53 337.8% 22.671 5388.77 0.00000 0.00000 19
2.6.32 8192 65536 16 61.75 668.9% 47.265 13271.37 0.12894 0.00000 9
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