Re: Disk cache

Arvid Norberg wrote:
> 
> On Apr 20, 2006, at 18:42, Radu Hociung wrote:
> 
>> Arvid Norberg wrote:
>>
>>>
>>> I was primarily thinking about your testbench.
>>
>>
>> Perhaps I don't understand what you're asking. What would you like to
>> use on a clean strace log?
>>
>> The only thing that my testbench does currently is to add a comment on
>> every _lseek, read and write line showing cumulative efficiency on  that
>> file descriptor, along with the position of the drive heads at the  time
>> the read/write call was made. These two pieces of information are only
>> used to plot the fancy graphs I've shown.
>>
>> You can certainly derive the same plots from a clean strace log, which
>> contains all the necessary information.
> 
> 
> Well, basically I would like to run the kinds of test that you did,  but
> on darwin. ang generate the graphs to see if any changes I've  made
> improves any performance.

That's cool.

The test setup I used initially is very simple, as you know (1 seed + 1
downloader).

I think the ktrace log file will be easy to use to plot the behaviour of
the client. You need to log lseeks, reads and writes.

If you plot the lseek location versus time or lseek number, you'll get
the access pattern. I plot write seeks and read seeks in different colour.

In order to plot the effectiveness curve, you need to calculate from the
logs the distance travelled while seeking, and the distance travelled
while read/writing. I calculate the effectiveness of accesses as the
ratio between distance travelled while read/writing and total distance
travelled. The wikipedia page I published earltier also contains details
about the calculations and measurements.

Let me know if I can help more.

Radu.


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