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From Dirk-Willem van Gulik <>
Subject Re: Holy FUD Batman!
Date Wed, 14 Apr 1999 07:31:16 GMT

Marc Slemko wrote:
> >The problem: the server performs well, delivering in excess of 1300 HTTP
> >GET requests per second. But then performance drops WAAAY off, like down
> >to 70 connections per second. We're not swapping, the network isn't
> >saturated (4 x 100Mbit nets), disks are hardly used, but the system is
> >just crawling. If it were saturated then performance should level off,
> >not drop like this. Neither vmstat nor top show anything unusual. No
> >error messages in the web server. Its puzzling.

Actually I have seen the same, specifically with RedHat 5.1. We kind of did not
had the time to investigate; so we installed FreeBSD, got rid of the problem,
and kind of schrugged (assuming it we should have spend a patch or something,
but we needed a <30minute solution :-( ). No swapping, no unusual behaviour 
except for two things; a lot of kernel time was spend in (ide) interup handling 
(even though the disk which counted are all scsi, i.e. swap and content; only
the boot disk was IDE) and the kernel buffers seemed allocated weirdly between 
tcp and exfs. The other thing which was confirming was the 'sharpness' of the cut-off
moment; which coincieded with the interupt going up; followed by the free kernel
buffer ditching. But then, I am no RH expert, so we might have done something 
way wrong. 


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