Re: [uml-devel] uml responsivenes or "AS vs DEADLINE Scheduler on uml-host" - was: [uml-user] Network lags

["roland" <for_spam@gmx.de>]

hi!

>1) Well, you switched from AS to deadline and got a significant IO performance
>improvement, which made UML faster since it was Disk-bound. The problem with
>AS is that it uses an heuristic, which assumes sequential reads.
mmhh - i didn`t really recognize that i got a big improvement of i/o performance
in general. i just recognized, that my uml was more responsive to ping (no more
"sendmsg: no buffer space available,no network lags of values like 60s anymore).
btw: my uml didn`t access the disk at all, while answering the pings (why should it?
all that network-stuff happens in uml-kernel space)

>But "find /" is very seeky, so it is slow with AS. So if you remove this bg
>thread, you should get significantly different results.
no - that doesn`t really matter. ok - it took some more time that i got network lags
with my uml and "sendmsg:..."-ping-errors. but the errors were the same and happened
regardless of the 10 parallel "find /" threads, i started on the host.

>Also, AS has had some changes in later kernels, so you should probably upgrade
>your host kernel to the latest version. A security hole (a local exploit to
thats a point. will try that if i find some time. does somebody have some more details
what was changed exactly? (i dont know much about bitkeeper - but maybe i can view the
changelog like in cvs, for every single file?)

>2) In your last email, you speak about hogging the UML CPU. If Jeff guessed
>correctly what happens, then avoiding that UML is idle will decrease the
>worst-case ping response times.
i think he guessed wrong. it doesnt matter if my uml is idle or not - no difference
if i run a vmstat (and some more) inside my uml( i.e. it is not idle) while pinging.
the effect i experience doesnt`t seem to be an effect which is caused by a uml being
swapped out and in again - because i didn`t see a single byte being swapped out/in on
the host. so this effect remains....strange for me.

regards
roland





----- Original Message ----- 
From: "BlaisorBlade" <blaisorblade_spam@yahoo.it>
To: "roland" <for_spam@gmx.de>; "Jeff Dike" <jdike@addtoit.com>
Cc: "Joern Bredereck" <jb@bw-networx.net>; <user-mode-linux-user@lists.sourceforge.net>;
<user-mode-linux-devel@lists.sourceforge.net>; <mingo@elte.hu>
Sent: Saturday, April 10, 2004 2:28 PM
Subject: Re: [uml-devel] uml responsivenes or "AS vs DEADLINE Scheduler on uml-host" - was: [uml-user] Network lags


Alle 20:33, venerdì 9 aprile 2004, roland ha scritto:
> Hi !
> I think i found an interesting "scheduling issue" which led me to switch
> the subject of the thread.

1) Well, you switched from AS to deadline and got a significant IO performance
improvement, which made UML faster since it was Disk-bound. The problem with
AS is that it uses an heuristic, which assumes sequential reads.

But "find /" is very seeky, so it is slow with AS. So if you remove this bg
thread, you should get significantly different results.

Also, AS has had some changes in later kernels, so you should probably upgrade
your host kernel to the latest version. A security hole (a local exploit to
become root) has also been fixed after 2.6.0.

2) In your last email, you speak about hogging the UML CPU. If Jeff guessed
correctly what happens, then avoiding that UML is idle will decrease the
worst-case ping response times.

-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729



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