Effects of Clearing the Cache on Benchmarks

How to win friends and influence benchmarks...

I note that I have a shell in my nc_test4 directory, clear_cache.sh. I have to sudo to run it, but when I do, it has a dramatic effect on the time that the time series read takes.

The following uses the new (not yet checked in) test program tst_ar4_3d.c, which seeks to set up a simpler proxy data file for the AR-4 tests. I want to show that a simpler file (but with the same-sized data variable) has similar performance to the slightly more dressed up pr_A1 file from AR-4 that I got from Gary. That's because my simpler file is easier to create in a test program.

bash-3.2$ ./tst_ar4_3d -h 
cs[0] cs[1] cs[2] cache(MB) deflate shuffle read_hor(us) read_time_ser(us)
64    256   128   4.0       0       0       1420         2281847
bash-3.2$ ./tst_ar4_3d -h cs[0] cs[1] cs[2] cache(MB) deflate shuffle read_hor(us) read_time_ser(us) 64    256   128   4.0       0       0       81           3159
bash-3.2$ ./tst_ar4_3d -h cs[0] cs[1] cs[2] cache(MB) deflate shuffle read_hor(us) read_time_ser(us) 64    256   128   4.0       0       0       76           2983
bash-3.2$ sudo bash clear_cache.sh
bash-3.2$ ./tst_ar4_3d -h cs[0] cs[1] cs[2] cache(MB) deflate shuffle read_hor(us) read_time_ser(us) 64    256   128   4.0       0       0      1410         2504315

Wow, what a difference a cleared cache makes!

Here's the clear_cache.sh script:

#!/bin/bash -x 
# Clear the disk caches.
sync
echo 3 > /proc/sys/vm/drop_caches

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