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Date:      Wed, 5 Mar 2003 01:42:05 +0200
From:      "Petri Helenius" <pete@he.iki.fi>
To:        "Bosko Milekic" <bmilekic@unixdaemons.com>
Cc:        <freebsd-current@FreeBSD.ORG>
Subject:   Re: mbuf cache
Message-ID:  <0e3701c2e2a7$aaa2b180$932a40c1@PHE>
References:  <0ded01c2e295$cbef0940$932a40c1@PHE> <20030304164449.A10136@unixdaemons.com> <0e1b01c2e29c$d1fefdc0$932a40c1@PHE> <20030304173809.A10373@unixdaemons.com> <0e2b01c2e2a3$96fd3b40$932a40c1@PHE> <20030304182133.A10561@unixdaemons.com>

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>
>   This does look odd... maybe there's a leak somewhere... does "in use"
>   go back down to a much lower number eventually?  What kind of test are
>   you running?  "in pool" means that that's the number in the cache
>   while "in use" means that that's the number out of the cache
>   currently being used by the system; but if you're telling me that
>   there's no way usage could be that high while you ran the netstat,
>   either there's a serious leak somewhere or I got the stats wrong
>   (anyone else notice irregular stats?)
>
I think I figured this, the "em" driver is allocating mbuf for each receive
descriptor regardless if it´s needed or not. Does this cause a performance
issue if there is 8000 mbufs in use and we get 100k-150k frees and
allocates a second (for every packet?)

(I have the em driver configured for 4096 receive descriptors)

>   Another thing I find odd about those stats is that you've set the high
>   watermark to 8192, which means that in the next free, you should be
>   moving buckets to the general cache... see if that's really
>   happening...  The low watermark doesn't affect anything right now.

Nothing seems to be moving to the GEN pool.
>
>   Can you give me more details on the exact type of test you're running?
>   Let's move this to -current instead of -current and -net please (feel
>   free to trim the one you want), getting 3 copies of the same
>   message all the time is kinda annoying. :-(
>
I´m running a snort-like application with the interface getting receive only
packets. It can either connect to a netgraph node or use bpf, both seem to have
similar performance (most CPU is used elsewhere) as the email I sent previously
had listed.

Pete


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