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SubjectRe: [PATCH] cfq-iosched: reduce write depth only if sync was delayed
Date
Corrado Zoccolo <czoccolo@gmail.com> writes:

> Hi Jeff,
> On Wed, Dec 9, 2009 at 7:09 PM, Jeff Moyer <jmoyer@redhat.com> wrote:
>> Corrado Zoccolo <czoccolo@gmail.com> 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.  The number of random operations defaults
>> to 4000, which is pretty low.  I'll re-run the tests with a number
>> comparable to the sequential runs.  Sorry about that.
>>
> N.P.

low_latency=1

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 19.35 26.10% 74.639 3278.74 0.00000 0.00000 74
2.6.32 8192 65536 16 20.40 53.07% 135.695 3705.55 0.00000 0.00000 38

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 64.64 342.2% 22.708 5960.22 0.00153 0.00000 19
2.6.32 8192 65536 16 61.19 663.7% 47.648 11294.56 0.16098 0.00000 9


low_latency=0

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 19.71 25.32% 70.891 4340.92 0.00000 0.00000 78
2.6.32 8192 65536 16 22.67 58.94% 121.669 6180.49 0.00229 0.00000 38

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 64.69 339.5% 22.651 6770.99 0.00152 0.00000 19
2.6.32 8192 65536 16 61.94 663.0% 46.962 10719.13 0.12741 0.00000 9


> if you have time, can you also re-run the test changing:
> iosched/fifo_expire_async to 8 ?

Sure.

Cheers,
Jeff
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