From: Sebastien Godard Date: Sun, 29 Jan 2012 14:28:42 +0000 (+0100) Subject: FAQ updated. X-Git-Tag: v10.0.4~4 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=50ec564fbdce084052c7844b84850e06bf9e2428;p=sysstat FAQ updated. A question and answer has been added for sar and for pidstat. --- diff --git a/CHANGES b/CHANGES index da3891a..66f81ab 100644 --- a/CHANGES +++ b/CHANGES @@ -5,6 +5,7 @@ xxxx/xx/xx: Version 10.0.4 - Sebastien Godard (sysstat orange.fr) sar -b results. * configure script updated: Added --disable-stripping option. Using this option tells configure to NOT strip object files. + * FAQ updated. * NLS updated. Serbian translation added. 2011/11/27: Version 10.0.3 - Sebastien Godard (sysstat orange.fr) diff --git a/FAQ b/FAQ index 197f6bf..ea105e8 100644 --- a/FAQ +++ b/FAQ @@ -53,6 +53,7 @@ Also tell me what version your kernel is). 2.21. The sar command displays some weird output values... 2.22. What happened to sar's options -h, -H, -x and -X? 2.23. What is the exact meaning of the parameter for sar and sadc? +2.24. Why doesn't sar deal with sub-second sampling/monitoring? 3. QUESTIONS RELATING TO IOSTAT @@ -72,6 +73,8 @@ Also tell me what version your kernel is). 4.2. The pidstat command complains with the following message: "Requested activities not available". 4.3. pidstat doesn't display statistics for process (task) xyz... +4.4. I noticed that the total CPU utilization for threads running on + an individual CPU can exceed 100%... 1. GENERAL QUESTIONS @@ -532,6 +535,26 @@ same output as sar -f 1 5. Note that it all depends on the number of data samples pre-existing in the data file. If the file is empty when first running sadc then the above is true. +~~ + +2.24. Why doesn't sar deal with sub-second sampling/monitoring? + +There are two reasons for sar to not handle sub-second intervals: + +1) This is not sar's purpose. sar has been created to give the +sys admin a global overview of its machine daily utilization so +that when a problem happens, he has a benchmark and can compare +the statistics gathered by sar with those saved before. For that +reason an interval of 10 minutes (which is the default for sar) is +quite appropriate. + +2) Because this is just a dumb idea to try to gather a huge amount +of data on a sub-second interval basis (and sar really collects +a lot of data). This can be resource-consuming and you are all the +more prone to have an influence on the data you are retrieving as +the interval of time is small. + + 3. QUESTIONS RELATING TO IOSTAT ############################### @@ -658,6 +681,17 @@ will display only tasks that have actually used some CPU resources since system startup. You should enter "pidstat -u -p ALL" to make sure that all the processes are listed in the report. +~~~ + +4.4. I noticed that the total CPU utilization for threads running on + an individual CPU can exceed 100%... + +The CPU number displayed by pidstat is the CPU to which the task is attached +when the statistics are actually displayed. This doesn't mean that the task +has spent its whole interval of time attached to it. Hence the CPU ressource +used by a thread on an interval of time as displayed by pidstat may have +concerned several processors. + -- Sebastien Godard (sysstat orange.fr) is the author and the current maintainer of this package.