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#uml IRC Logs for 2007-05-31

---Logopened Thu May 31 00:00:21 2007
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08:03<jdike>Hi guys
08:18<jdike>So, I was wondering why UML performance sucked so badly all of a sudden
08:18<jdike>a 6.5 minute kernel build was now taking 30
08:18<jdike>I checked both my main development trees - they both did the same thing
08:19<jdike>starting to wonder about the host kernel, since I've been playing with it
08:20<jdike>then I remembered booting it with 32M because this guy yesterday was complaining about that not working
08:21<jdike>sure enough, that's what was in my command history, and I was just finding the last UML boot command and running it without looking at it
08:25<mikegrb>:>
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10:41<LemyDanger>hello
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10:45<LemyDanger>is it better to compile the host with high mem supprot ? i have have 1 GB on the machine
10:47<jdike>32-bit host?
10:47<LemyDanger>yes
10:47<jdike>I guess, but 1G is pretty marginal
10:49<LemyDanger>unfortunately i cant upgrade
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10:53<kokoko1>Hello guys
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10:59[~]jdike puts printks in userspace code
10:59<jdike>that won't work so well
11:35<peterz>heh, just put a printk wrapper in your userspace libs :-)
11:57<jdike>hehe
11:59<kokoko1>Firstly don't panic! :-)
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12:10<linux__alien>hello jdike
12:13<linux__alien>couldnt log on to my system for the past 2 days. I am not able to copy a file from my host kernel to UML using scp . Its unable to locate my file
12:13<linux__alien>but the file exists in the same path
12:13<jdike>what's the scp command?
12:16<linux__alien>scp 10.1.1.5@localhost:/home/balaji/zebra-0.95a.tar.gz .
12:16<linux__alien>this command i am giving it in UML
12:16<linux__alien>10.1.1.5 is the IP address of tap0 interface in host kernel
12:16<peterz>linux__alien: you seem confused
12:16<peterz>linux__alien: you gave 2 hosts
12:16<linux__alien>2 hosts how ?
12:16<linux__alien>:-o
12:16<peterz>ip@host
12:17<peterz>the syntax is user@host:path
12:17<jdike>do you understand scp?
12:17<linux__alien>ve not used it at all
12:17<linux__alien>didnt get a chance to use it
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12:24<linux__alien>instead of shutting down UML did that in my host kernel and my machine halted :-)
12:24<jdike>why are you on the host as root at all?
12:25<linux__alien>no actually in that shell alone i had logged in as root and this happened
12:26<linux__alien>:-)
12:26<linux__alien>from UML can i connect to the tap0 interface in the host?
12:26<linux__alien>scp balaji@10.1.1.5:/home/balaji/zebra-0.95a.tar.gz .
12:26<linux__alien>sh: connect to host 10.1.1.5 port 22: Connection refused
12:26<linux__alien>i get this error
12:26<jdike>what normally causes that?
12:27<linux__alien>sorry SSH was not running started that
12:29<linux__alien>have a doubt wont i be in a position to execute telnet from inside UML?
12:30<jdike>is telnetd running on the host?
12:31<linux__alien>i dont have telnetd in my host
12:32<linux__alien>ve sshd though
12:32<jdike>well, telnetd running wherever you want to telnet to
12:33<linux__alien>you mean to say that i should have telnetd running wherever i want to telnet to is it
12:34<jdike>yeah
12:35<linux__alien>jdike, ok so now have couple of questions. I ve extracted my tar package but when i did ./configure it said no gcc and exited so now for me to install gcc is there any easy method here ? and where do i get that telnetd from
12:35<jdike>you know about yum?
12:36<linux__alien>yes
12:36<linux__alien>ve used it also
12:36<linux__alien>but thats in host right ?
12:38<jdike>what do you know about yum?
12:39<linux__alien>with yum you can install rpm packages . The advantage of yum is that it checks for dependencies and installs the packages too from the internet
12:39<jdike>right!
12:40<jdike>so, what do you think about using yum to install gcc?
12:40<linux__alien>yes ve done that too in my host but how do i do it in UML
12:40<linux__alien>infact i upgraded my Gcc in Fedora 6 using yum . yum update gcc
12:41<linux__alien>so you want me to compile the package in Host and move the binaries alone to UML is it?
12:41<linux__alien>is that what you mean by any chance?
12:42<jdike>you have a fedora filesystem booted in UML, right?
12:42<linux__alien>yes
12:42<linux__alien>ok thats got yum just checked
12:42<linux__alien>it but somehow internet does not work in UML :-)
12:42<jdike>well, you should fix that
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12:42<linux__alien>oh...
12:45<linux__alien>Ok thanks jdike Will play with it. Thanks for your inputs.
12:50<linux__alien>cya
12:50<linux__alien>all
12:50<linux__alien>have a nice day
12:50<linux__alien>bye
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12:50<peterz>jdike: you're so patient
12:50<jdike>hehe
12:50<jdike>amazing cluelessness
12:51<peterz>yes, looks like a microsoftie's first encounter with a unix cli
12:51<jdike>and no ability to recognize sarcasm
12:51<peterz>lol
12:52<peterz>he's from india
12:53<peterz>it might be a language/cultural barrier for sarcasm
12:54<jdike>maybe
12:54<jdike>the Brits say the same thing about us
12:54<peterz>us being usaians I take it :-)
12:55[~]peterz notes he lives on the same side of the big pond as those quaint brits
12:56<jdike>right
13:00[~]jdike sends off a batch of syslet demo patches
13:00<peterz>you've been playing with syslets?
13:01<jdike>yup
13:01<peterz>to make uml go faster?
13:01<jdike>yup
13:01<peterz>and did it?
13:01<jdike>patience, grasshopper
13:01<peterz>hehe
13:02<jdike>I wrote a couple small demos to understand the interface
13:02<peterz>I take it its mostly the batching of syscalls thats interresting
13:02<jdike>no
13:02<jdike>but that's interesting for later
13:03<jdike>the interesting part is that syslets can be used to collect status on all async events in which UML is interested
13:03<jdike>disk I/O
13:03<jdike>timer expirations
13:03<jdike>child process status
13:03<jdike>all in one loop, with no interrupts
13:04<peterz>nice
13:04<jdike>the syscall batching is interesting as a skas4 mechanism
13:04<peterz>the extended epoll interface can do some of those too
13:04<peterz>they have signalfd and timerfds 'n stuff
13:05<jdike>yeah, but it can't automatically background something which is going to block
13:05<jdike>while immediately returning for something which is available now
13:05<peterz>right, but each uml process has its own thread, right?
13:05<jdike>right now, yes, but they won't use this
13:06<jdike>the kernel threads use it, and they need to worry about what's synchronous and what's not
13:06<peterz>right, and with these syslets thats fixed
13:06<peterz>is it bounded?
13:06<jdike>right
13:07<jdike>you mean the asynchronousness?
13:07<peterz>yeah
13:07<peterz>at some point spawning more syslets will not make things better
13:07<jdike>yeah
13:07<jdike>there's a fixed number of async threads
13:08<peterz>nice
13:08[~]peterz obviously hasn't read all those syslet emails
13:08<peterz>perhaps I should
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13:12<jdike>if I add new_mm() and switch_mm() system calls, I can use the batching mechanism to fiddle process address spaces with
13:13<jdike>batch( switch_mm(proc_mm), mmap, munmap, mprotect, etc, etc, switch_mm(my_mm) )
13:13<peterz>yeah, that'd save a bunch of ctx
13:14<jdike>and possibly a bunch of tlb flushes
13:14<peterz>right, those might be even more interesting
13:14<peterz>those suckers are expensive
13:14<jdike>but that would need some more surgery
13:16<jdike>but the attraction is that new_mm/switch_mm looks to me like a reasonable interface
13:16<peterz>yeah, you tried that before, right?
13:17<jdike>the batching allows the whole sequence to be automated in the kernel
13:17[~]peterz lost on intel.com
13:17<jdike>which is nice since doing anything immediately after switching address spaces is problematic
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13:20<jdike>and off goes one bug fix in the async stuff itself
13:25<peterz>darn, I wrote myself an non obvious infinite loop
13:55<dgraves>peterz: awesome!
13:55<peterz>dgraves: yeah, some days.. :-)
13:56<peterz>basically: while (!(foo >> shift)) { shift += c; }
13:57<peterz>s/!//
13:57<dgraves>how is that infinite? shouldn't foo left shifted by shift eventually = 0?
13:58<dgraves>right shifted
13:58<peterz>compiler translates that into sar %cl, %edx
13:58<peterz>and cl gets masked by 31
13:59<peterz>if 32 mod c != 0
13:59<peterz>you'll never get a full shift
13:59<dgraves>what's sar?
13:59<peterz>and hence never terminate
13:59<peterz>shift right
13:59<dgraves>peterz: wow. that is unobvious.
13:59<jdike>shift arithmetic right
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---Logclosed Fri Jun 01 00:00:56 2007