serial problems cont..

serial problems cont..

[Michael Malone]

Hi everyone,

I've written a couple of questions regarding the serial device in KVM.  
After slightly more investigation I think I have found what's going 
awry.  Correct me if I'm wrong, but I believe that KVM generates an 
interrupt for every single character it sends through the serial port.  
This throws CPU usage through the roof and I suspect this means that the 
timers aren't being handled correctly and it failed on a string of 0's 
for me due to the timing slips.  GNU/Linux and Windows don't have 
anywhere near the processor usage for their serial ports.  Now, I know 
nothing of serial programming and don't have any time to investigate it 
too heavily just now, but I have pulled down the source and had a look 
through that, but it looks to be doing the right thing (I suppose?).   I 
was mainly wondering how GNU/Linux and windows handle serial interrupts 
or if some of the serial character events could be buffered, rather than 
overload the processor?  I guess this is a low priority for you, but any 
help would be greatly appreciated (And when I have some more time, I 
will spend some of it helping to develop KVM! Quid pro quo, Clarice...)

Thanks,

Michael

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Re: serial problems cont..

[Avi Kivity]

Michael Malone wrote:
> Hi everyone,
>
> I've written a couple of questions regarding the serial device in 
> KVM.  After slightly more investigation I think I have found what's 
> going awry.  Correct me if I'm wrong, but I believe that KVM generates 
> an interrupt for every single character it sends through the serial 
> port.  This throws CPU usage through the roof and I suspect this means 
> that the timers aren't being handled correctly and it failed on a 
> string of 0's for me due to the timing slips.  GNU/Linux and Windows 
> don't have anywhere near the processor usage for their serial ports.  
> Now, I know nothing of serial programming and don't have any time to 
> investigate it too heavily just now, but I have pulled down the source 
> and had a look through that, but it looks to be doing the right thing 
> (I suppose?).   I was mainly wondering how GNU/Linux and windows 
> handle serial interrupts or if some of the serial character events 
> could be buffered, rather than overload the processor?  I guess this 
> is a low priority for you, but any help would be greatly appreciated 
> (And when I have some more time, I will spend some of it helping to 
> develop KVM! Quid pro quo, Clarice...)
>

What version of kvm are you testing?  There were some changes to the 
serial emulation recently.  See for example 
02f0b4c0cc26f3a2578d515d96781f5a6258888d in kvm-73.

-- 
error compiling committee.c: too many arguments to function

Re: serial problems cont..

[Michael Malone]

Avi Kivity wrote:
> Michael Malone wrote:
>> Hi everyone,
>>
>> I've written a couple of questions regarding the serial device in 
>> KVM.  After slightly more investigation I think I have found what's 
>> going awry.  Correct me if I'm wrong, but I believe that KVM 
>> generates an interrupt for every single character it sends through 
>> the serial port.  This throws CPU usage through the roof and I 
>> suspect this means that the timers aren't being handled correctly and 
>> it failed on a string of 0's for me due to the timing slips.  
>> GNU/Linux and Windows don't have anywhere near the processor usage 
>> for their serial ports.  Now, I know nothing of serial programming 
>> and don't have any time to investigate it too heavily just now, but I 
>> have pulled down the source and had a look through that, but it looks 
>> to be doing the right thing (I suppose?).   I was mainly wondering 
>> how GNU/Linux and windows handle serial interrupts or if some of the 
>> serial character events could be buffered, rather than overload the 
>> processor?  I guess this is a low priority for you, but any help 
>> would be greatly appreciated (And when I have some more time, I will 
>> spend some of it helping to develop KVM! Quid pro quo, Clarice...)
>>
>
> What version of kvm are you testing?  There were some changes to the 
> serial emulation recently.  See for example 
> 02f0b4c0cc26f3a2578d515d96781f5a6258888d in kvm-73.
>
I have tried with kvm 62, 69, 72 and 74.  All of them gave the same 
result.  What do you mean by "See for example 
02f0b4c0cc26f3a2578d515d96781f5a6258888d"?
- I am running Ubuntu 8.04 (Hardy) as host and Windows XP as guest on an 
Intel Core 2 duo processor.

=======================================================================
This email, including any attachments, is only for the intended
addressee.  It is subject to copyright, is confidential and may be
the subject of legal or other privilege, none of which is waived or
lost by reason of this transmission.
If the receiver is not the intended addressee, please accept our
apologies, notify us by return, delete all copies and perform no
other act on the email.
Unfortunately, we cannot warrant that the email has not been
 altered or corrupted during transmission.
=======================================================================

Re: serial problems cont..

[Avi Kivity]

Michael Malone wrote:
>>
>> What version of kvm are you testing?  There were some changes to the 
>> serial emulation recently.  See for example 
>> 02f0b4c0cc26f3a2578d515d96781f5a6258888d in kvm-73.
>>
> I have tried with kvm 62, 69, 72 and 74.  All of them gave the same 
> result.  What do you mean by "See for example 
> 02f0b4c0cc26f3a2578d515d96781f5a6258888d"?
> - I am running Ubuntu 8.04 (Hardy) as host and Windows XP as guest on 
> an Intel Core 2 duo processor.

I meant 
http://git.kernel.org/?p=linux/kernel/git/avi/kvm-userspace.git;a=commit;h=02f0b4c0cc26f3a2578d515d96781f5a6258888d 
.  But since it doesn't seem to solve your problems (it is part of 
kvm-74), more work is needed.

-- 
error compiling committee.c: too many arguments to function