Linux 2.6.38 Kernel Multi-Core Scaling

[phoronix]

Phoronix: Linux 2.6.38 Kernel Multi-Core Scaling

Last month there were benchmarks on Phoronix looking at the multi-core scaling performance of multiple operating systems, including CentOS 5.5, Fedora 14, FreeBSD 8.1, and OpenIndiana b148. CentOS 5.5 uses the long-term Linux 2.6.18 kernel while Fedora 14 has the more recent Linux 2.6.35 kernel by default, but a number of users asked how the Linux 2.6.38 kernel would fair for multi-core scaling with the removal of the Big Kernel Lock and various other low-level improvements in this forthcoming kernel. Here are some benchmarks showing just that.

http://www.phoronix.com/vr.php?view=15753

[devius]

Shouldn't this be tested on something with a really big number of cores/processors to be able to see any differences? Something like 48 cores or more? 6 cores isn't all that much, even if they have HT.

[mtippett]

The 48 core systems will be 4x12 cores. That's a slightly different (and expensive scenario).

This system represents a single package high core count - which is arguably going to be the typical mid-high end system that people will be getting for the next year or so.

What is interesting is that Ubuntu did get a reasonable gain from 6 real cores to 12 cores (6 being HT). The PC-BSD and OpenIndiana systems would typically collapse when HT was turned on. You get the benefit of about 1-2 _real_ cores with the 6 HT "cores" being enabled.

[HokTar]

The 48 core systems will be 4x12 cores. That's a slightly different (and expensive scenario).

Yes, but this scenario is typical for small-scale Linux-based clusters which are typically used for engineering / scientific calculations thus it is of interest to many of us.
But I do get your point and unfortunately I can't donate a system like that so the situation is unlikely to change. Maybe you could ask Tyan or Supermicro for the reasons I mentioned.

[jakubo]

comments on the graphs are rare these days on phoronix.com
nothing to tell why the big kernel lock patch and the "patch that does wonders" - as proclaimed - hardly make a change?

[mtippett]

comments on the graphs are rare these days on phoronix.com
nothing to tell why the big kernel lock patch and the "patch that does wonders" - as proclaimed - hardly make a change?

It depends on where the contention lies. For heavy CPU-only loads, the BKL won't immediately yield any difference. When you start getting into heavy IO multi-threaded IO heavy loads, the waiting within the kernel becomes critical. This IO load can be graphics, disk or network.

Different benchmarks will have different sensitivity.

[mtippett]

Yes, but this scenario is typical for small-scale Linux-based clusters which are typically used for engineering / scientific calculations thus it is of interest to many of us.
But I do get your point and unfortunately I can't donate a system like that so the situation is unlikely to change. Maybe you could ask Tyan or Supermicro for the reasons I mentioned.

I'm expecting that it will come. Although I doubt that the scalability testing will be done by the vendors, having results from those systems are fully expected.

[Smorg]

IDK, The way Intel likes to never ever lower the prices on their higher-end consumer grade chips (i.e. gulftown), and with the relatively low cost of entry-level dual socket boards it might be a very logical upgrade path to grab yourself a second low-end i7 chip and go for a NUMA xeon setup. I'll take a 16-thread NUMA configuration over a $1000 12-thread single-socket gulftown.

[kraftman]

Shouldn't this be tested on something with a really big number of cores/processors to be able to see any differences? Something like 48 cores or more? 6 cores isn't all that much, even if they have HT.

The improvements should be even visible even on 4 cores. Thanks for the test Michael. I wonder why there's no difference? Maybe some funny stuff is disabled or something?

[kraftman]

comments on the graphs are rare these days on phoronix.com
nothing to tell why the big kernel lock patch and the "patch that does wonders" - as proclaimed - hardly make a change?

Weren't those patches aiming at responsiveness?