Re: [Xen-devel] [PATCH for 4.7 0/4] Assorted scheduling fixes

[Meng Xu <mengxu@xxxxxxxxxxxxx>]

Hi Wei,

On Wed, May 4, 2016 at 12:04 PM, Wei Liu <wei.liu2@xxxxxxxxxx> wrote:
>
> On Tue, May 03, 2016 at 11:46:27PM +0200, Dario Faggioli wrote:
> > Hi,
> >
> > This small series contains some bugfixes for various schedulers. They're all
> > bugfixes, so I think all should be considered for 4.7. Here's some more
> > detailed analysis.
> >
> > Patch 1 and 3 are for Credit2. Patch 1 is a lot more important, as we have 
> > an
> > ASSERT triggering without it. Patch 2 is behavioral fixing, which I believe 
> > it
> > is important, but at least does not make anything explode.
> >
> > Patch 2 fixes another ASSERT, in case a pCPU fails to come up. This is what
> > Julien reported here:
> >
> >  https://www.mail-archive.com/xen-devel@xxxxxxxxxxxxx/msg65918.html
> >
> > Julien, the patch is very very similar to the one attached to one of my 
> > reply
> > in that thread, but I had to change some small bits... Can you please 
> > re-test
> > it?
> >
> > Patch 4 makes the code of RTDS look consistent with what we state in patch 
> > 2,
> > so it's also important. Furthermore, it does fix a bug (although, again, not
> > one that would splat Xen) as, without it, we may have a timer used by the 
> > RTDS
> > scheduler bound to the pCPU of another cpupool with another scheduler. That
> > would introduce some unwanted and very difficult to recognize interference
> > between different schedulers in different pool, and should hence be avoided.
> >
> > So this was awesomeness; about risks:
> >  - patch 1 is very small, super-self contained (zero impact outside of 
> > Credit2
> >    code) and it fixes an actual and 100% reproducible bug;
> >  - patch 2 is also totally self-contained and it can't possibly cause 
> > problems
> >    to anything else than to what it is trying to fix (Credit2's load 
> > balancer).
> >    It doesn't cure any ASSERT or Oops, so it's less interesting, but given 
> > the
> >    low risk --also considering that Credit2 will still be considered
> >    experimental in 4.7-- I think it can go in;
> >  - patch 3 is bigger, and a bit more complex. Note, however, that most of 
> > its
> >    content is code comments and ASSERT-s; it is self contained to scheduling
> >    (in the sense that it impacts all schedulers, but "just" them), and fixes
> >    a situation that, AFAIUI, is important for ARM;
>
> You meant patch 2 actually.
>
> For the first three patches:
>
> Release-acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
>
> >  - patch 4 may again look not that critical. But, the fact that someone 
> > wanting
> >    to experiment with RTDS in a cpupool would face the kind of interference
> >    between independent cpupools that the patch cures is, I think, something
> >    worthwhile trying to avoid.


Yes. It's better to avoid this type of interference.


>
> Besides, it is again quite self contained, as
> >    it's indeed only relevant for RTDS (which is also going to be called
> >    experimental for 4.7).


Yes. It should not affect other schedulers or other parts of the system.
Actually, it does not affect the logic in RTDS either.


> I will wait for Meng to review this one.


I just reviewed and tested this patch on my computer.
Thank you very much!

Best regards,

Meng

-----------
Meng Xu
PhD Student in Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~mengxu/

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel