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Commit 8b48206e authored by Teng Qin's avatar Teng Qin Committed by GitHub
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Merge pull request #2178 from brendangregg/tools 

cachestat: bring back HITRATIO column
parents 41ffdd17 6af7b844
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man/man8/cachestat.8
View file @ 8b48206e
...@@ -18,18 +18,14 @@ Since this uses BPF, only the root user can use this tool. ...@@ -18,18 +18,14 @@ Since this uses BPF, only the root user can use this tool.
CONFIG_BPF and bcc. CONFIG_BPF and bcc.
.SH EXAMPLES .SH EXAMPLES
.TP .TP
Print summaries every five second: Print summaries every second:
# #
.B cachestat .B cachestat
.TP .TP
Print summaries every five seconds with timestamp: Print summaries every second with timestamp:
# #
.B cachestat -T .B cachestat -T
.TP .TP
Print summaries each second:
#
.B cachestat 1
.TP
Print output every five seconds, three times: Print output every five seconds, three times:
# #
.B cachestat 5 3 .B cachestat 5 3
...@@ -51,6 +47,9 @@ Number of page cache misses. ...@@ -51,6 +47,9 @@ Number of page cache misses.
DIRTIES DIRTIES
Number of dirty pages added to the page cache. Number of dirty pages added to the page cache.
.TP .TP
HITRATIO
The hit ratio as a percentage.
.TP
READ_HIT% READ_HIT%
Read hit percent of page cache usage. Read hit percent of page cache usage.
.TP .TP
......
tools/cachestat.py
View file @ 8b48206e
...@@ -15,6 +15,7 @@ ...@@ -15,6 +15,7 @@
# 09-Sep-2015 Brendan Gregg Created this. # 09-Sep-2015 Brendan Gregg Created this.
# 06-Nov-2015 Allan McAleavy # 06-Nov-2015 Allan McAleavy
# 13-Jan-2016 Allan McAleavy run pep8 against program # 13-Jan-2016 Allan McAleavy run pep8 against program
# 02-Feb-2019 Brendan Gregg Column shuffle, bring back %ratio
from __future__ import print_function from __future__ import print_function
from bcc import BPF from bcc import BPF
...@@ -55,7 +56,7 @@ parser = argparse.ArgumentParser( ...@@ -55,7 +56,7 @@ parser = argparse.ArgumentParser(
formatter_class=argparse.RawDescriptionHelpFormatter) formatter_class=argparse.RawDescriptionHelpFormatter)
parser.add_argument("-T", "--timestamp", action="store_true", parser.add_argument("-T", "--timestamp", action="store_true",
help="include timestamp on output") help="include timestamp on output")
parser.add_argument("interval", nargs="?", default=5, parser.add_argument("interval", nargs="?", default=1,
help="output interval, in seconds") help="output interval, in seconds")
parser.add_argument("count", nargs="?", default=-1, parser.add_argument("count", nargs="?", default=-1,
help="number of outputs") help="number of outputs")
...@@ -102,7 +103,7 @@ b.attach_kprobe(event="mark_buffer_dirty", fn_name="do_count") ...@@ -102,7 +103,7 @@ b.attach_kprobe(event="mark_buffer_dirty", fn_name="do_count")
if tstamp: if tstamp:
print("%-8s " % "TIME", end="") print("%-8s " % "TIME", end="")
print("%8s %8s %8s %8s %12s %10s" % print("%8s %8s %8s %8s %12s %10s" %
("TOTAL", "MISSES", "HITS", "DIRTIES", "BUFFERS_MB", "CACHED_MB")) ("HITS", "MISSES", "DIRTIES", "HITRATIO", "BUFFERS_MB", "CACHED_MB"))
loop = 0 loop = 0
exiting = 0 exiting = 0
...@@ -121,38 +122,36 @@ while 1: ...@@ -121,38 +122,36 @@ while 1:
counts = b["counts"] counts = b["counts"]
for k, v in sorted(counts.items(), key=lambda counts: counts[1].value): for k, v in sorted(counts.items(), key=lambda counts: counts[1].value):
func = b.ksym(k.ip)
if re.match(b'mark_page_accessed', b.ksym(k.ip)) is not None: # partial string matches in case of .isra (necessary?)
if func.find("mark_page_accessed") == 0:
mpa = max(0, v.value) mpa = max(0, v.value)
if func.find("mark_buffer_dirty") == 0:
if re.match(b'mark_buffer_dirty', b.ksym(k.ip)) is not None:
mbd = max(0, v.value) mbd = max(0, v.value)
if func.find("add_to_page_cache_lru") == 0:
if re.match(b'add_to_page_cache_lru', b.ksym(k.ip)) is not None:
apcl = max(0, v.value) apcl = max(0, v.value)
if func.find("account_page_dirtied") == 0:
if re.match(b'account_page_dirtied', b.ksym(k.ip)) is not None:
apd = max(0, v.value) apd = max(0, v.value)
# total = total cache accesses without counting dirties # total = total cache accesses without counting dirties
# misses = total of add to lru because of read misses # misses = total of add to lru because of read misses
total = (mpa - mbd) total = mpa - mbd
misses = (apcl - apd) misses = apcl - apd
if misses < 0:
if total < 0: misses = 0
total = 0 if total < 0:
total = 0
if misses < 0: hits = total - misses
misses = 0
# If hits are < 0, then its possible misses are overestimated
hits = total - misses # due to possibly page cache read ahead adding more pages than
# needed. In this case just assume misses as total and reset hits.
# If hits are < 0, then its possible misses are overestimated if hits < 0:
# due to possibly page cache read ahead adding more pages than misses = total
# needed. In this case just assume misses as total and reset hits. hits = 0
if hits < 0: ratio = 0
misses = total if total > 0:
hits = 0 ratio = float(hits) / total
if debug: if debug:
print("%d %d %d %d %d %d %d\n" % print("%d %d %d %d %d %d %d\n" %
...@@ -167,18 +166,10 @@ while 1: ...@@ -167,18 +166,10 @@ while 1:
if tstamp: if tstamp:
print("%-8s " % strftime("%H:%M:%S"), end="") print("%-8s " % strftime("%H:%M:%S"), end="")
print("%8d %8d %8d %8d %12.0f %10.0f" % print("%8d %8d %8d %7.2f%% %12.0f %10.0f" %
(total, misses, hits, mbd, buff, cached)) (hits, misses, mbd, 100 * ratio, buff, cached))
mpa = 0 mpa = mbd = apcl = apd = total = misses = hits = cached = buff = 0
mbd = 0
apcl = 0
apd = 0
total = 0
misses = 0
hits = 0
cached = 0
buff = 0
if exiting: if exiting:
print("Detaching...") print("Detaching...")
......
tools/cachestat_example.txt
View file @ 8b48206e
# ./cachestat -h Demonstrations of cachestat, the Linux eBPF/bcc version.
USAGE: ./cachestat [-T] [ interval [count] ]
show Linux page cache hit/miss statistics including read and write hit %
cachestat shows hits and misses to the file system page cache. For example:
# cachestat
HITS MISSES DIRTIES HITRATIO BUFFERS_MB CACHED_MB
1132 0 4 100.00% 277 4367
161 0 36 100.00% 277 4372
16 0 28 100.00% 277 4372
17154 13750 15 55.51% 277 4422
19 0 1 100.00% 277 4422
83 0 83 100.00% 277 4421
16 0 1 100.00% 277 4423
^C 0 -19 360 0.00% 277 4423
Detaching...
While tracing, there was a burst of misses in the fourth second, bringing
the hit ration down to 55%.
This shows a 1 Gbyte uncached file that is read twice:
(root) ~ # ./cachestat.py
HITS MISSES DIRTIES HITRATIO BUFFERS_MB CACHED_MB
1 0 0 100.00% 5 191
198 12136 0 1.61% 5 238
1 11007 3 0.01% 5 281
0 6384 0 0.00% 5 306
1 14464 0 0.01% 5 363
0 11776 0 0.00% 5 409
1 11712 0 0.01% 5 454
32 13184 0 0.24% 5 506
0 11232 0 0.00% 5 550
1 13056 0 0.01% 5 601
16 14720 0 0.11% 5 658
33 9920 0 0.33% 5 697
0 13248 0 0.00% 5 749
4 14144 0 0.03% 5 804
0 9728 0 0.00% 5 842
1 10816 0 0.01% 5 885
808 13504 1 5.65% 5 938
0 11409 0 0.00% 5 982
0 11520 0 0.00% 5 1027
0 15616 0 0.00% 5 1088
1 9792 0 0.01% 5 1126
0 8256 0 0.00% 5 1158
1 9600 0 0.01% 5 1196
599 4804 0 11.09% 5 1215
1 0 0 100.00% 5 1215
0 0 0 0.00% 5 1215
3 1 0 75.00% 5 1215
79536 34 0 99.96% 5 1215
87693 274 4 99.69% 6 1214
89018 3546 0 96.17% 7 1227
33531 201 4 99.40% 7 1228
22 44 0 33.33% 8 1228
0 0 0 0.00% 8 1228
73 21 2 77.66% 8 1228
It took 24 seconds to read the 1 Gbyte file the first time, shown in the output
by the high MISSES rate and low HITRATIO. The second time it took 4 seconds,
and the HITRATIO was around 99%.
This output shows a 1 Gbyte file being created and added to the page cache:
(root) ~ # ./cachestat.py
HITS MISSES DIRTIES HITRATIO BUFFERS_MB CACHED_MB
1 0 0 100.00% 8 209
0 0 165584 0.00% 8 856
0 0 96505 0.00% 8 1233
0 0 0 0.00% 8 1233
Note the high rate of DIRTIES, and the CACHED_MD size increases by 1024 Mbytes.
USAGE message:
# cachestat -h
usage: cachestat.py [-h] [-T] [interval] [count]
Count cache kernel function calls
positional arguments:
interval output interval, in seconds
count number of outputs
optional arguments: optional arguments:
-T include timestamp on output -h, --help show this help message and exit
-T, --timestamp include timestamp on output
examples:
./cachestat # run with default option of 5 seconds delay
./cachestat -T # run with default option of 5 seconds delay with timestamps
./cachestat 1 # print every second hit/miss stats
./cachestat -T 1 # include timestamps with one second samples
./cachestat 1 5 # run with interval of one second for five iterations
./cachestat -T 1 5 # include timestamps with interval of one second for five iterations
Following commands show a 2GB file being read into the page cache.
Command used to generate activity:
# dd if=/root/tmpfile of=/dev/null bs=8192
Output from cachestat running simultatenously:
# ./tools/cachestat.py 1
TOTAL MISSES HITS DIRTIES BUFFERS_MB CACHED_MB
1 0 1 0 8 283
0 0 0 0 8 283
0 0 0 2 8 283
0 0 0 0 8 283
10009 9173 836 2 9 369
152032 152032 0 0 9 1028
157408 157405 3 0 9 1707
150432 150432 0 0 9 2331
0 0 0 0 9 2331
1 1 0 1 9 2331
0 0 0 0 9 2331
0 0 0 0 9 2331
0 0 0 0 9 2331
The misses counter reflects a 2GB file being read and almost everything being
a page cache miss.
Below shows an example of a new 100MB file added to page cache, by using
the command: dd if=/dev/zero of=/root/tmpfile2 bs=4k count=$((256*100))
# ./tools/cachestat.py 1
TOTAL MISSES HITS DIRTIES BUFFERS_MB CACHED_MB
0 0 0 0 15 2440
0 0 0 0 15 2440
0 0 0 0 15 2440
1758 0 1758 25603 15 2540
0 0 0 0 15 2540
0 0 0 0 15 2541
~25600 pages are being dirtied (writes) which corresponds to the 100MB file
added to the page cache.
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