[CentOS] Kernel update = slower ?

[Sam Drinkard]

William L. Maltby wrote:

>On Sun, 2006-06-04 at 09:57 -0400, Sam Drinkard wrote:
>  
>
>>William L. Maltby wrote:
>>
>>    
>>
>>>On Thu, 2006-06-01 at 19:18 -0400, Sam Drinkard wrote:
>>> 
>>>
>>>      
>>>
>>>>Johnny,
>>>>
>>>>   After reading about the VM issue, I concur. <snip>
>>>>        
>>>>
>
>  
>
>>>I forget the start of this thread... was 64 bit only? Anyway, I had my
>>>32bit lock a couple times with symptoms like Sam mentions. Lots of swap
>>>used and no reason for it. Was using lots of open browsers, a couple
>>>different GUI MUAs, etc.
>>>
>>>Turned off things I didn't need <snip>
>>>      
>>>
>
>  
>
>>>A *biggie*, maybe, is the stupid readahead and readahead_early stuff.
>>><snip>
>>>      
>>>
>
>  
>
>>>Up now for 6 days running similar load (I think, haven't bothered to
>>>really measure it) and swap use is still good and response is still
>>>good.
>>><snip>
>>>      
>>>
>
>  
>
>>After uptime of a little over 3 days now, I'm not seeing any increase in 
>>swap as I did prior, but then again, I don't exactly recall how long it 
>>took before swap started increasing.
>>    
>>
>
>For my symptoms to appear, it took a combo of time up and an increase in
>load. Don't know if this is coincidence or cause and effect.
>
>  
>
>>One thing I do notice is for some 
>>reason, the applications that nomally would consume between 1.2 - 1.4G 
>>of memory is now down to 1.1 - 1.2, and swap is only lightly touched at 
>>181mb.
>>    
>>
>
>Again, mine is only a workstation, so I don't know how this applies to
>you. My max on the previous session was 64k into swap. That was about 4
>days up, IIRC and I tried at several points to dupe the conditions
>(opened several browsers, multiple users, several different
>type/instances of MUAs, several ssh to my LAN server, etc.).
>
>I've since turned sendmail back on so I can do some LAN-internal things
>with it. Pretty much stock config except that I removed the restriction
>on localhost (a DAEMON_OPTION in the sendmail.mc file). Needed to reboot
>to to test LVM config changes (new stuff for me) and after a day and a
>half of running, 0k in swap with medium load.
>
>  
>
>>Don't know if this is due to the kernal update or what, but it 
>>would seem logical that it is, since I see different behavior than 
>>previously.  I've not turned off readahead or readahead_early yet, but 
>>will do so shortly and see if I can tell any difference in model run 
>>times which did increase after the kernel update.  One thing at a time I 
>>guess :-)
>>    
>>
>
>Theoretically, there ought to be a decrease in startup times at certain
>points _early_in_the_uptime_cycle. IMO, after a "steady state" typical
>loading is achieved (hours, day, weeks??) there should be no or reduced
>improvement (maybe decreased too *if* this forces some spurious swap
>activity?).
>
>*If* your config is anything similar to mine (or any generic?), I doubt
>you'll find any long-term gain significant enough to warrant even the
>near-zero maintenance of two more scripts and associated files.
>
>It's the old "It doesn't cost me anything, but I get no benefit either"
>routine. I almost always opt for excision of the wart. Sometimes that
>costs later, but that's OK by me.
>
>  
>
>
Just before the current model run started, I turned off the readahead 
and readahead_early, and see a considerable decrease in used memory, 
down from 1.2G to about 975 +/-.  Unfortunately, the model did not 
initialize on time, and I had to bring it up manualy after some input 
files were not available, but I can tell by runtime if there has been 
any improvement.  Normal runtime is about 3.75 hours, and *any* 
reduction in runtime would be great.  This machine is set up as a 
workstation, with X and the whole nine yards going, but there are no 
entertainment things used, nor word processing, etc.  The only mail is 
what I get from the system too, however sendmail is alive and active.  I 
do have things set if my primary mail machine goes down, I can enable 
Evolution on it with a mouse click.  There are no other users except for 
an ocassional login from a friend who assists in some of the software 
running that I am unfamilar with at this point.  I do see some processes 
that could probably be turned off, but as long as I  don't start hitting 
swap and thrashing disks, there probably would be no benefit in real 
terms to stop these services, and some, I'm not sure I fully understand 
what all is taking place either.  Currently 150 processes and a load 
aveage of 2.32, 2.10, and 2.04 give or take a little. 

We'll see what happens this afternoon when the model completes.  I'm 
hoping for good results.

-- 
Sam W.Drinkard -- sam at wa4phy.net
http://wa4phy.net
Augusta Area Mesonet
cell 706.825.8513 Home 706.868.7253
MAIL 4428 Branchwood Drive,
Martinez Georgia, 30907-1304