Re: [Xen-devel] [Patch 2 of 2]: PV-domain SMP performance Linux-part

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Mon, Jan 12, 2009 at 12:55 PM, Juergen Gross
<juergen.gross@xxxxxxxxxxxxxxxxxxx> wrote:
> Conclusion:
> -----------
> Differences not really big, but my "no deschedule" patch had least elapsed
> time for build-jobs, while scp was able to transfer same amount of data as
> in slower original system.
> The "Yield in spinlock" patch had slightly better dbench performance, but
> interactive shell commands were a pain sometimes! I suspect some problem in
> George's patches during low system load to be the main reason for this
> behaviour. Without George's patches the "Yield in spinlock" was very similar
> to the original system.

Hmm, the shell performance is a little worrying.  There may be
something strange going on...

Without my patches (at least, without the "yield reduces priority"
patch), "yield" is basically a no-op, so "yield in spinlock" is
functionally equivalent to the original system.

According to your numbers, the "user time" and "system time" were
exactly the same (only 0.6 seconds longer on system time), even though
the overall build took 52 seconds longer.  Is it possible that the
"yield" patches actually made it run less often?

scp works over tcp, which is often sensitive to latency; so it's
possible that the lowered priority on yield caused "hiccoughs", both
in the scp connections, and the interactive shell performance.

Anyway, I'll be looking into it after doing a scheduler update.

Peace,
 -George

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