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Commit 2b348704 authored by Joel Fernandes's avatar Joel Fernandes
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tools/cachestat: Rewrite it so it makes more sense 

cachstat separation between read and writes doesn't make much sense. During tests
its seen that a workload that is supposed to be completely in the missed category
appears to be 50% hit.

This patch rewrites the BCC tool to be more inline with Brendan Gregg's original
cachestat perf tool which makes more sense:
https://github.com/brendangregg/perf-tools/blob/master/fs/cachestat
http://www.brendangregg.com/blog/2014-12-31/linux-page-cache-hit-ratio.html

Fixes Issue: #1586
Signed-off-by: default avatarJoel Fernandes <joelaf@google.com>
parent cab4d7c6
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Showing with 66 additions and 91 deletions
tools/cachestat.py
View file @ 2b348704
......@@ -39,16 +39,13 @@ def get_meminfo():
return result
# set global variables
rtaccess = 0
wtaccess = 0
mpa = 0
mbd = 0
apcl = 0
apd = 0
access = 0
total = 0
misses = 0
rhits = 0
whits = 0
hits = 0
debug = 0
# args
......@@ -116,9 +113,8 @@ b.attach_kprobe(event="mark_buffer_dirty", fn_name="do_count")
# header
if tstamp:
print("%-8s " % "TIME", end="")
print("%8s %8s %8s %10s %10s %12s %10s" %
("HITS", "MISSES", "DIRTIES",
"READ_HIT%", "WRITE_HIT%", "BUFFERS_MB", "CACHED_MB"))
print("%8s %8s %8s %8s %12s %10s" %
("TOTAL", "MISSES", "HITS", "DIRTIES", "BUFFERS_MB", "CACHED_MB"))
loop = 0
exiting = 0
......@@ -150,28 +146,29 @@ while 1:
if re.match(b'account_page_dirtied', b.ksym(k.ip)) is not None:
apd = max(0, v.value)
# access = total cache access incl. reads(mpa) and writes(mbd)
# misses = total of add to lru which we do when we write(mbd)
# and also the mark the page dirty(same as mbd)
access = (mpa + mbd)
misses = (apcl + apd)
# total = total cache accesses without counting dirties
# misses = total of add to lru because of read misses
total = (mpa - mbd)
misses = (apcl - apd)
# rtaccess is the read hit % during the sample period.
# wtaccess is the write hit % during the smaple period.
if mpa > 0:
rtaccess = float(mpa) / (access + misses)
if apcl > 0:
wtaccess = float(apcl) / (access + misses)
if total < 0:
total = 0
if wtaccess != 0:
whits = 100 * wtaccess
if rtaccess != 0:
rhits = 100 * rtaccess
if misses < 0:
misses = 0
hits = total - misses
# If hits are < 0, then its possible misses are overestimated
# 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 < 0:
misses = total
hits = 0
if debug:
print("%d %d %d %d %d %d %f %f %d %d\n" %
(mpa, mbd, apcl, apd, access, misses,
rtaccess, wtaccess, rhits, whits))
print("%d %d %d %d %d %d %d\n" %
(mpa, mbd, apcl, apd, total, misses, hits))
counts.clear()
......@@ -182,21 +179,18 @@ while 1:
if tstamp == 1:
print("%-8s " % strftime("%H:%M:%S"), end="")
print("%8d %8d %8d %9.1f%% %9.1f%% %12.0f %10.0f" %
(access, misses, mbd, rhits, whits, buff, cached))
print("%8d %8d %8d %8d %12.0f %10.0f" %
(total, misses, hits, mbd, buff, cached))
mpa = 0
mbd = 0
apcl = 0
apd = 0
access = 0
total = 0
misses = 0
rhits = 0
hits = 0
cached = 0
buff = 0
whits = 0
rtaccess = 0
wtaccess = 0
if exiting:
print("Detaching...")
......
tools/cachestat_example.txt
View file @ 2b348704
......@@ -15,61 +15,42 @@ examples:
./cachestat -T 1 5 # include timestamps with interval of one second for five iterations
# ./cachestat 1
HITS MISSES DIRTIES READ_HIT% WRITE_HIT% BUFFERS_MB CACHED_MB
0 58 0 0.0% 100.0% 0 11334
146113 0 0 100.0% 0.0% 0 11334
244143 0 0 100.0% 0.0% 0 11334
216833 0 0 100.0% 0.0% 0 11334
248209 0 0 100.0% 0.0% 0 11334
205825 0 0 100.0% 0.0% 0 11334
286654 0 0 100.0% 0.0% 0 11334
275850 0 0 100.0% 0.0% 0 11334
272883 0 0 100.0% 0.0% 0 11334
261633 0 0 100.0% 0.0% 0 11334
252826 0 0 100.0% 0.0% 0 11334
235253 70 3 100.0% 0.0% 0 11335
204946 0 0 100.0% 0.0% 0 11335
0 0 0 0.0% 0.0% 0 11335
0 0 0 0.0% 0.0% 0 11335
0 0 0 0.0% 0.0% 0 11335
Above shows the reading of a 12GB file already cached in the OS page cache and again below with timestamps.
# ./cachestat -T 1
TIME HITS MISSES DIRTIES READ_HIT% WRITE_HIT% BUFFERS_MB CACHED_MB
16:07:10 0 0 0 0.0% 0.0% 0 11336
16:07:11 0 0 0 0.0% 0.0% 0 11336
16:07:12 117849 0 0 100.0% 0.0% 0 11336
16:07:13 212558 0 0 100.0% 0.0% 0 11336
16:07:14 302559 1 0 100.0% 0.0% 0 11336
16:07:15 309230 0 0 100.0% 0.0% 0 11336
16:07:16 305701 0 0 100.0% 0.0% 0 11336
16:07:17 312754 0 0 100.0% 0.0% 0 11336
16:07:18 308406 0 0 100.0% 0.0% 0 11336
16:07:19 298185 0 0 100.0% 0.0% 0 11336
16:07:20 236128 0 0 100.0% 0.0% 0 11336
16:07:21 257616 0 0 100.0% 0.0% 0 11336
16:07:22 179792 0 0 100.0% 0.0% 0 11336
Command used to generate the activity
# dd if=/root/mnt2/testfile of=/dev/null bs=8192
1442795+0 records in
1442795+0 records out
11819376640 bytes (12 GB) copied, 3.9301 s, 3.0 GB/s
Below shows the dirty ratio increasing as we add a file to the page cache
# ./cachestat.py
HITS MISSES DIRTIES READ_HIT% WRITE_HIT% BUFFERS_MB CACHED_MB
1074 44 13 94.9% 2.9% 1 223
2195 170 8 92.5% 6.8% 1 143
182 53 56 53.6% 1.3% 1 143
62480 40960 20480 40.6% 19.8% 1 223
7 2 5 22.2% 22.2% 1 223
348 0 0 100.0% 0.0% 1 223
0 0 0 0.0% 0.0% 1 223
0 0 0 0.0% 0.0% 1 223
0 0 0 0.0% 0.0% 1 223
0 0 0 0.0% 0.0% 1 223
The file copied into page cache was named 80m with a size of 83886080 (83886080/4096) = 20480, this matches what we see under dirties
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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