Scan Rates Post: 302307784

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Operating Systems AIX Scan Rates Post 302307784 by zaxxon on Thursday 16th of April 2009 10:29:18 AM

04-16-2009

Registered User

3k pages as scan rate per sec is no big value. I sometimes see bigger ones. Usually it's the ratio/relation between scanned pages and freed pages that matters. Optimal to ok should be ratio fr/sr of ~ 1:1 - 1:3 afaik; can be but must not.

From some IBM AIX Performance Management Guide, note the last line in bold letters:

Quote:

# fr

Number of pages that were freed per second by the page-replacement algorithm during the interval. As the VMM page-replacement routine scans the Page Frame Table (PFT), it uses criteria to select which pages are to be stolen to replenish the free list of available memory frames. The criteria include both kinds of pages, working (computational) and file (persistent) pages. Just because a page has been freed, it does not mean that any I/O has taken place. For example, if a persistent storage (file) page has not been modified, it will not be written back to the disk. If I/O is not necessary, minimal system resources are required to free a page.
# sr

Number of pages that were examined per second by the page-replacement algorithm during the interval. The VMM page-replacement code scans the PFT and steals pages until the number of frames on the free list is at least the maxfree value. The page-replacement code might have to scan many entries in the PFT before it can steal enough to satisfy the free list requirements. With stable, unfragmented memory, the scan rate and free rate might be nearly equal. On systems with multiple processes using many different pages, the pages are more volatile and disjoint. In this scenario, the scan rate might greatly exceed the free rate.

Memory is over committed when the ratio of fr to sr (fr:sr) is high.

An fr:sr ratio of 1:4 means that for every page freed, four pages had to be examined. It is difficult to determine a memory constraint based on this ratio alone, and what constitutes a high ratio is workload/application dependent.

For tuning in general and to get a first impression, you should look at the output from "vmstat 1 20" for example at busy times. Just looking at "sr" will show/mean nothing.

zaxxon

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LEARN ABOUT REDHAT

iwlist

IWLIST(8)						     Linux Programmer's Manual							 IWLIST(8)

NAME

       iwlist - Get wireless statistics from specific nodes

SYNOPSIS

       iwlist interface freq
       iwlist interface ap
       iwlist interface scan
       iwlist interface rate
       iwlist interface key
       iwlist interface power
       iwlist interface txpower
       iwlist interface retry
       iwlist --help
       iwlist --version

DESCRIPTION

       Iwlist is used to display some large chunk of information from a wireless network interface that is not displayed by iwconfig. This is typ-
       ically list of parameters.

PARAMETERS

       freq/channel
	      Give the list of available frequencies in the device and the number of defined channels. Please note that usually the driver returns
	      the  total  number  of  channels and only the frequencies available in the present locale, so there is no one to one mapping between
	      frequencies displayed and channel numbers.

       ap/accesspoint
	      Give the list of Access Points in range, and optionally the quality of link to them. This feature is obsolte and now  deprecated	in
	      favor of scanning support (below), and it will disappear in the future.

       scan[ning]
	      Give  the  list  of Access Points and Ad-Hoc cells in range, and optionally a whole bunch of information about them (ESSID, Quality,
	      Frequency, Mode...). The type of information returned depend on what the card support.
	      Triggering scanning is a priviledged operation (root only) and normal users can only read letf-over scan results.  By  default,  the
	      way  scanning  is done (the scope of the scan) will be impacted by the current setting of the driver. Also, this command is supposed
	      to take extra arguments to control the scanning behaviour, but this is currently not implemented.

       rate/bit[rate]
	      List the bit-rates supported by the device.

       key/enc[ryption]
	      List the encryption key sizes supported and display all the encryption keys availables in the device.

       power  List the various Power Management attributes and modes of the device.

       txpower
	      List the various Transmit Power available on the device.

       retry  List the transmit retry limits and retry lifetime on the device.

       --version
	      Display the version of the tools, as well as the recommended and current Wireless Extensions version for the tool  and  the  various
	      wireless interfaces.

FILES

       /proc/net/wireless

SEE ALSO

       iwconfig(8), ifconfig(8), iwspy(8).  iwpriv(8).

net-tools							  31 October 1996							 IWLIST(8)