Re: [Xen-devel] Re: [RFC][Patch] Improvemet the responce of xend.

[Akio Takebe <takebe_akio@xxxxxxxxxxxxxx>]

Hi,

Thank you for your comments.

>A few comments:
>
>a.   The patch basically spawn a new process to handle the additional "xm" 
>inputs asynchronously.   Correct? 
Yes, but currently only at the time of dump-core.

>  And since currently this is not possible
>, it also means that the possibilities of deadlocks or race conditions 
>through concurrent access to xend via different xm users is not thoroughly 
>verified.   Correct?   May be.   So this is something to look out for.
>
I don't understand completely what you said.
Basicaly xend work one by one,
so if xm requests dump-core, xend work only for it.
I think it is difficult to change xend to multi thread.
But because dump-core work is very simple,
Xend should be able to let another process do dump-core work.

When I posted my patch, I had a mistake that I don't open socket for xenstore.
Now we're making another patch with other approach.
If xend get a dump-core request, xend does fork() and exec(xc_dump)
(like xc_save, xc_restore). 
If the child process wants to write something into xensotre,
it can do by using xs_daemon_open(), xs_write() and so on. (I think)

We concern with what we should do if another xm request destory
to the dumped domain.

>b.   The performance of dump core is slow, mainly because external hard disk
> are slow.   Therefore, there could be four different options/variations:   
>minidump vs full-dump.   For each there could be a compressed vs no-
>compression option - compressed is to get a smaller physical core.   
>
Yes, I also think so and want their options.
But I don't think the performance yet.

>c.   Furthermore, there could be an additional throttling parameters to 
>specify how much to slow the coredump operation, for example, by forcing a 
>CPU re-scheduling operation (higher overheads in task switching - tradeoff 
>for responsiveness) after every fix number of blocks.   This will also have 
>the effect of improving performance for additional domU's operation.
We may be able to do it by nice command
if xend let another process do dump-core work.

Best Regards,

Akio Takebe


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