Re: [Xen-devel] planned csched improvements?

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Sat, Oct 17, 2009 at 1:16 AM, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
> Incidentally, I've been thinking of a schedular plugin for database and
> other similar apps. Prelimanary DB benchmarks on xen vs bare metal are
> not as good. Of course, I am not blaming schedular for it. As with most
> big user apps, DB is very multi-threaded, and as such it does lot of
> tricks to get the OS schedular to play it it's way.
> I may be getting my hands on a large box in few weeks to bring up xen
> and do some scalability work. Hope to find some low hanging fruit.

Scalability for Xen past 8 logical processors (where 1 hyperthread is
1 schedulable unit) is likely to be poor, due to the load-balancing
algorithm.

Regarding a Xen scheduler plug-in for DB applications, it seems to me
it would be best to understand the characteristics of the DB workload
and how they respond to different kinds of contention.  There may be a
few surprises; for example, a workload that you assumed was CPU-bound
may in fact be making many qemu-handled operations, so it's really
blocking thousands of times per second.  If we can make the default
scheduler handle DB workloads well without making a special plug-in,
that would be preferrable.

Would you be willing, if you have the time, to help "beta-test" a new
scheduler with a DB workload and compare it to the old one?

 -George

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