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

Florian Haas florian.haas at linbit.com
Thu Jan 10 15:18:21 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 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 G. Haas
: LINBIT Information Technologies GmbH
: Vivenotgasse 48, A-1120 Vienna, Austria

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