[linux-mm-cc] Re: Some testings using ccache pre-alpha 003 for i386

[Nitin Gupta]

Hi,

Please see new page posted on project home page: 
http://linuxcompressed.sourceforge.net/braindumps
I have detailed here possible explanation for these negative results.

I hope to have some solutions implemented soon :)

Cheers,
Nitin


Anderson Briglia wrote:
> Hi all,
>
> I did some tests using the latest ccache code posted by Nitin Gupta. I
> divided the tests in two types: Memory behavior and time performance.
> All tests had this scenario:
>
> - linus kernel 2.6.18-rc4 with ccache pre-alpha 003 applied
> - qemu with ubuntu-dapper image
> - 128MB of RAM
> - No Swap devices
> - After every test, the machine was rebooted
>
> Memory Behavior
> -----------------------------------------------------------
> This test intends to evaluate what happens on the system when it has a
> high memory load. What is the ccache impact? Is it stable even the
> free memory is critical low?
> To do this test I used memtest 0.0.4 [1], that is a suite of tests
> developed to evaluate the stability and consistency of the Linux
> memory management system. It is composed of some testing programs but
> I used just one test, called fillmem. Fillmem tests the memory
> allocation system. It is useful to check the virtual memory system
> face allocation memory, pagination and swap usage. As its parameter,
> fillmem receives the size of the memory that will be allocated.
>
> fillmem50-ccache1000.gif (graph01) attached file represents the memory
> when executed fillmem with 50MB of parameter and ccache with 1000
> pages of size.
> fillmem50-no-ccache.gif (graph02) attached file represents the memory
> when executed fillmem with 50MB as well, but without ccache.
> The x axis represents the time in seconds and the y axis the memory in
> kilobytes. Make a comparison between the two graphs, we can see that
> the ccache adds a overhead because the test spends more time to
> allocate and free the same memory size. And we have also the number of
> AnonPages increased. Maybe due the metadata needed for the ccache
> control.
> One more thing is, 1000 pages as ccache size are not enough to improve
> the memory allocation. I didn't use a bigger ccache size because it's
> not stable yet and the system just freezes if the ccache is bigger (>
> 10MB for example). Discussing with Nitin, he said me that it's
> something related to the LRU active list handling. He is investigating
> this problem.
>
> Time Performance
> --------------------------------------------------------
> This test intends to evaluate the ccache overhead when executing the
> memory test and an application. I selected the Firefox startup to
> measure. Just called firefox at the command line with 'time' to do the
> measurements. The same way was used to measure the time when executing
> the fillmem test.
>
> fillmem-test-time.gif attached file represents the time measurement
> when executing the fillmem test discussed above. As you can see, the
> test is much more faster (almost 3 times) without ccache. I believe it
> is expected once we naturally have an overhead to use the ccache
> system: all those chunk's operations, vswap control, etc...
>
> firefox-startup[01-02].gif attached files represent the time spent to
> load firefox. On this test, I executed firefox two times without
> reboot the machine. I was expecting a gain on the speed when using
> ccache, once we should have more 'firefox anonpages' in the memory
> when using ccache. But as we can see, we don't have a big difference
> when using and not using the ccache. But the startup was faster when
> ccache was used.
>
> Conclusion
> ------------------------------------------------------
> I believe that it's early to take some conclusion of the ccache
> benefits. More use cases must be developed and tested to check the
> impact and improvements of it. We just have a pre-alpha version and we
> have to focus on fix the bugs to have a 'real workable' ccache
> version.
>
> References
> -----------------------------------------------------
> [1] Memtest Suite. <http://carpanta.dc.fi.udc.es/~quintela/memtest/>
>
>
> Best regards,
>
> Anderson Briglia
> Open Source Mobile Research Center - Embedded Linux Lab
> Instituto Nokia de Tecnologia - INdT - Manaus/Brazil
>
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