Messages in this thread | | | Date | Thu, 27 Sep 2012 07:18:15 +0200 | From | Borislav Petkov <> | Subject | Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to 3.6-rc5 on AMD chipsets - bisected |
| |
On Thu, Sep 27, 2012 at 07:09:28AM +0200, Mike Galbraith wrote: > > The way I understand it is, you either want to share L2 with a process, > > because, for example, both working sets fit in the L2 and/or there's > > some sharing which saves you moving everything over the L3. This is > > where selecting a core on the same L2 is actually a good thing. > > Yeah, and if the wakee can't get to the L2 hot data instantly, it may be > better to let wakee drag the data to an instantly accessible spot.
Yep, then moving it to another L2 is the same.
[ … ]
> > A crazy thought: one could go and sample tasks while running their > > timeslices with the perf counters to know exactly what type of workload > > we're looking at. I.e., do I have a large number of L2 evictions? Yes, > > then spread them out. No, then select the other core on the L2. And so > > on. > > Hm. That sampling better be really cheap. Might help...
Yeah, that's why I said sampling and not run the perfcounters during every timeslice.
But if you count the proper events, you should be able to know exactly what the workload is doing (compute-bound, io-bound, contention, etc...)
> but how does that affect pgbench and ilk that must spread regardless > of footprints.
Well, how do you measure latency of the 1 process in the 1:N case? Maybe pipeline stalls of the 1 along with some way to recognize it is the 1 in the 1:N case.
Hmm.
-- Regards/Gruss, Boris. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |