CPU affinity optimization, 8.2 vs. 8.0 (was Re: [DRBD-user] drbd-8.2.3.tar.gz and gitweb online)

Art Age Software artagesw at gmail.com
Fri Jan 11 00:40:58 CET 2008

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Jan 10, 2008 6:18 AM, Florian Haas <florian.haas at linbit.com> wrote:
> On Thursday 10 January 2008 15:08:05 Philipp Reisner wrote:
> > On Wednesday 09 January 2008 19:08:31 Art Age Software wrote:
> > > * Significant latency improvement: Implemented sane default
> > >   CPU bindings (affinity mask) of threads, and added the tuning
> > >   option 'cpu-mask'.
> > >
> > > Any chance of rolling this enhancement into the 8.0 series? I
> > > currently have my own script to set the cpu affinity. But it would be
> > > much nicer and cleaner to use a facility built into drbd.
> >
> > We have to draw somewhere the line, what to do in 8.0 and what to do in
> > 8.2. The tuning option will not come to 8.0, but as a side effect of a
> > change to come we will get sane default cpu masks in 8.0 as well.
> Adding to that. The modifications that Phil refers to as "sane default CPU
> masks" greatly reduce CPU cache misses within DRBD. So that's going to reduce
> latency in and of itself. However, without the cpu-mask option (and a taskset
> command for your mysqld), MySQL and DRBD will still be competing for CPU
> resources, and you're unlikely to a reduction of context switches. So in your
> case you would be benefiting from only one half of the latency improvements
> just added to 8.2.3. And, you don't get online verification. So, what's
> forcing you to stick with 8.0?
> Florian

Good question. For one thing, I am under the impression that 8.0 is
the more "stable" branch and that potentially risky new features might
be added to 8.2 still. So, for a production system, 8.2 is not
feasible for me.

For another,  I am sticking to what's available as a pre-packaged RPM
for CentOS 5. This currently limits me to the 8.0 branch.

Which leads me to another suggestion. I think it would be great if you
opened up your prepackaged binaries to a wider audience. I cannot
afford a full support contract. But I would be willing to pay a modest
amount for an annual subscription to the pre-built binary packages
(albeit without any additional support). I bet this would be a popular
option for many other users as well. Just a thought.


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