4 ms·

Running these two commands in series is likely vastly overstating the performance gains - almost all your time is going to be spent in io, and the second time a

by mattj 18y ago

Running these two commands in series is likely vastly overstating the performance gains - almost all your time is going to be spent in io, and the second time around you'll have a good chunk (if not all) of it in disk cache. Try running both a few repeated times and see if you enjoy the same gains (on my iphone right now, so I can't do this myself)

delano 18y ago
You are correct sir! $ time find . -newerct '10 hours ago' -print real 0m4.262s user 0m0.090s sys 0m1.014s $ time find . -newerct '10 hours ago' -print real 0m0.516s user 0m0.057s sys 0m0.251s $ time find . -newerct '10 hours ago' -print real 0m0.302s user 0m0.056s sys 0m0.244s $ time find . -newerct '10 hours ago' -print real 0m0.311s user 0m0.057s sys 0m0.251s $ find . | wc -l 13167 Is there a way to reliably flush the disk cache besides restarting?
- jws 18y ago
  Speaking of Linux, yes. You can echo mysterious numbers into /proc/sys/vm/drop_caches to flush various caches. http://jim.studt.net/depository/index.php/flushing-caches-for-benchmarking-in-linux http://jim.studt.net/depository/index.php/flushing-caches-fo... for a one liner, http://linux-mm.org/Drop_Caches http://linux-mm.org/Drop_Caches for the info from the horse's mouth. As an example, consider running md5sum on a directory of 1436 jpeg files of about 50k each on an Atom 330 ( 2 dies, 2 hyperthreads/die). The 8way numbers use xargs with -n8 and -P8. The flushed cache entries indicate that all three caches have been flushed immediately before the command ... elapsed user system Cold cache: 11.98 0.56 1.75 ======================== second run: 2.71 1.38 1.76 ===== third run: 3.17 1.40 1.75 ====== flushed cache: 12.11 0.58 1.80 ======================== flushed cache, 8way: 12.64 1.00 2.27 ========================= second run, 8way: 1.22 1.15 2.52 == third run, 8way: 1.17 1.26 2.26 == I do not explain the oddity that user time seems abnormally low with flushed cache, or perhaps abnormally high with cache data present, particularly with the single threaded version.
  - delano 18y ago
    Great, thanks. What did you use to generate that output?
    - jws 18y ago
      'time', and typing. The graph bars are my right index finger while I count in my head. I should probably patent that before it gets out. Wait, I just published. I'm screwed.
      - prewett 18y ago
        You have a year after first publication to patent. But you have successfully prevented anyone else from patenting (unless they already applied).

by mattj 18y ago

delano 18y ago

You are correct sir! $ time find . -newerct '10 hours ago' -print real 0m4.262s user 0m0.090s sys 0m1.014s $ time find . -newerct '10 hours ago' -print real 0m0.516s user 0m0.057s sys 0m0.251s $ time find . -newerct '10 hours ago' -print real 0m0.302s user 0m0.056s sys 0m0.244s $ time find . -newerct '10 hours ago' -print real 0m0.311s user 0m0.057s sys 0m0.251s $ find . | wc -l 13167 Is there a way to reliably flush the disk cache besides restarting?

jws 18y ago
Speaking of Linux, yes. You can echo mysterious numbers into /proc/sys/vm/drop_caches to flush various caches. http://jim.studt.net/depository/index.php/flushing-caches-for-benchmarking-in-linux http://jim.studt.net/depository/index.php/flushing-caches-fo... for a one liner, http://linux-mm.org/Drop_Caches http://linux-mm.org/Drop_Caches for the info from the horse's mouth. As an example, consider running md5sum on a directory of 1436 jpeg files of about 50k each on an Atom 330 ( 2 dies, 2 hyperthreads/die). The 8way numbers use xargs with -n8 and -P8. The flushed cache entries indicate that all three caches have been flushed immediately before the command ... elapsed user system Cold cache: 11.98 0.56 1.75 ======================== second run: 2.71 1.38 1.76 ===== third run: 3.17 1.40 1.75 ====== flushed cache: 12.11 0.58 1.80 ======================== flushed cache, 8way: 12.64 1.00 2.27 ========================= second run, 8way: 1.22 1.15 2.52 == third run, 8way: 1.17 1.26 2.26 == I do not explain the oddity that user time seems abnormally low with flushed cache, or perhaps abnormally high with cache data present, particularly with the single threaded version.
- delano 18y ago
  Great, thanks. What did you use to generate that output?
  - jws 18y ago
    'time', and typing. The graph bars are my right index finger while I count in my head. I should probably patent that before it gets out. Wait, I just published. I'm screwed.
    - prewett 18y ago
      You have a year after first publication to patent. But you have successfully prevented anyone else from patenting (unless they already applied).