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SubjectRe: BFS vs. mainline scheduler benchmarks and measurements
On 09/09/2009 09:04 PM, Ingo Molnar wrote:
> [...]
> * Jens Axboe<jens.axboe@oracle.com> wrote:
>
>> On Wed, Sep 09 2009, Jens Axboe wrote:
>> [...]
>> BFS210 runs on the laptop (dual core intel core duo). With make -j4
>> running, I clock the following latt -c8 'sleep 10' latencies:
>>
>> -rc9
>>
>> Max 17895 usec
>> Avg 8028 usec
>> Stdev 5948 usec
>> Stdev mean 405 usec
>>
>> Max 17896 usec
>> Avg 4951 usec
>> Stdev 6278 usec
>> Stdev mean 427 usec
>>
>> Max 17885 usec
>> Avg 5526 usec
>> Stdev 6819 usec
>> Stdev mean 464 usec
>>
>> -rc9 + mike
>>
>> Max 6061 usec
>> Avg 3797 usec
>> Stdev 1726 usec
>> Stdev mean 117 usec
>>
>> Max 5122 usec
>> Avg 3958 usec
>> Stdev 1697 usec
>> Stdev mean 115 usec
>>
>> Max 6691 usec
>> Avg 2130 usec
>> Stdev 2165 usec
>> Stdev mean 147 usec
>
> At least in my tests these latencies were mainly due to a bug in
> latt.c - i've attached the fixed version.
>
> The other reason was wakeup batching. If you do this:
>
> echo 0> /proc/sys/kernel/sched_wakeup_granularity_ns
>
> ... then you can switch on insta-wakeups on -tip too.
>
> With a dual-core box and a make -j4 background job running, on
> latest -tip i get the following latencies:
>
> $ ./latt -c8 sleep 30
> Entries: 656 (clients=8)
>
> Averages:
> ------------------------------
> Max 158 usec
> Avg 12 usec
> Stdev 10 usec

With your version of latt.c, I get these results with 2.6-tip vs
2.6.31-rc9-bfs:


(mainline)
Averages:
------------------------------
Max 50 usec
Avg 12 usec
Stdev 3 usec

(BFS)
Averages:
------------------------------
Max 474 usec
Avg 11 usec
Stdev 16 usec

However, the interactivity problems still remain. Does that mean it's
not a latency issue?


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