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Diffstat (limited to 'cddl/contrib/dtracetoolkit/Examples/diskhits_example.txt')
| -rw-r--r-- | cddl/contrib/dtracetoolkit/Examples/diskhits_example.txt | 107 |
1 files changed, 107 insertions, 0 deletions
diff --git a/cddl/contrib/dtracetoolkit/Examples/diskhits_example.txt b/cddl/contrib/dtracetoolkit/Examples/diskhits_example.txt new file mode 100644 index 0000000..6fe3a85 --- /dev/null +++ b/cddl/contrib/dtracetoolkit/Examples/diskhits_example.txt @@ -0,0 +1,107 @@ +The following is a demonstration of the diskhits command. + + +Here we run diskhits on a large file, /extra1/contents with is 46 Mb, and +currently hasn't been accessed (so isn't in any cache). + +While diskhits is running, the file is grep'd in another window. This causes +the entire file to be read, + + # ./diskhits /extra1/contents + Tracing... Hit Ctrl-C to end. + ^C + Location (KB), + + value ------------- Distribution ------------- count + < 0 | 0 + 0 |@@ 47 + 2303 |@@ 41 + 4606 |@@ 41 + 6909 |@@ 42 + 9212 |@@ 41 + 11515 |@@ 41 + 13818 |@@ 42 + 16121 |@@ 43 + 18424 |@@ 42 + 20727 |@@ 41 + 23030 |@@ 41 + 25333 |@@ 41 + 27636 |@@ 41 + 29939 |@@ 42 + 32242 |@@ 44 + 34545 |@@ 41 + 36848 |@@ 41 + 39151 |@@ 41 + 41454 |@@ 41 + 43757 |@@ 40 + >= 46060 | 0 + + Size (KB), + + value ------------- Distribution ------------- count + 4 | 0 + 8 | 6 + 16 | 10 + 32 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 818 + 64 | 0 + + Total RW: 46064 KB + +Ok, so the file was read evently with each access around 32 to 63 Kb in size, +and a total of 46 Mb read. This all makes sense, as it is reading the file +for the first time. + + + +Now the same file is grep'd with diskhits running, this time we can see what +effect caching the file has made, + + # ./diskhits /extra1/contents + Tracing... Hit Ctrl-C to end. + ^C + Location (KB), + + value ------------- Distribution ------------- count + 2303 | 0 + 4606 | 5 + 6909 |@ 67 + 9212 |@@@@ 170 + 11515 |@@@@@ 216 + 13818 |@@@@@ 224 + 16121 |@@@@@@ 287 + 18424 |@@@@@ 227 + 20727 |@@@ 144 + 23030 |@@ 75 + 25333 |@ 59 + 27636 |@ 42 + 29939 |@ 41 + 32242 |@ 44 + 34545 |@ 41 + 36848 |@ 41 + 39151 |@ 41 + 41454 |@ 41 + 43757 |@ 39 + >= 46060 | 0 + + Size (KB), + + value ------------- Distribution ------------- count + 2 | 0 + 4 |@@@@@@@@@@@@@@@@@@@@@@@@@ 1137 + 8 |@@@@@ 211 + 16 |@@ 111 + 32 |@@@@@@@@ 345 + 64 | 0 + + Total RW: 29392 KB + +The difference is dramatic. This time only 29 Mb is read, leaving around +17 Mb that was read from the cache. The way the file is read differs - +in the later half of the file it looks the same, but in the first half there +are many more events; oddly enough, this is because the early part of the +file is cached more, the extra events are likely to be much smaller in size - +as indicated in the difference in the size distribution. + +It appears that everything less that 4606 Kb has remained in the cache, with +zero hits for that range. + |
