Well, this settles it for me

Posted Sep 7, 2009 7:32 UTC (Mon) by bvdm (guest, #42755)
In reply to: Well, this settles it for me by yoshi314
Parent article: BFS vs. mainline scheduler benchmarks and measurements

Firstly, Linux has a very small desktop presence, so not entirely optimizing for the desktop is a rational design decision, though "totally disconnected" is very hard to swallow.

Secondly, one hardly wants to re-implement something like a scheduler every year. Designing for the near and medium future creates stability. Anyway, you would be hard pressed to find a desktop machine without at least 2 cores these days.

As for netbooks, if interactivity (people keep posting about gaming FPS and high-def audio and high-res desktop experience) is such a concern, why are you using a netbook? A typical netbook has far fewer processes running.

I don't think there ever was a "war". It is a shame that so much unproductive drama was generated by someone who is evidently skillful at performing for the peanut gallery.

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Well, this settles it for me

Posted Sep 7, 2009 7:44 UTC (Mon) by k8to (guest, #15413) [Link] (3 responses)

In conversations among engineers throughout silicon valley who have reason to push their code into or hack on Linux, the view of the LKML as unworkably hostile, short sighted, and unwilling to accept external ideas is now the norm. This is essentially a complete reversal from 10 years ago when people viewed it as relatively open and inviting.

Yes, this is subjective and I'm sure it has noise. I think it's also the truth.

Well, this settles it for me

Posted Sep 7, 2009 7:45 UTC (Mon) by k8to (guest, #15413) [Link]

Ie. I think this is the "totally disconnected" angle.

Well, this settles it for me

Posted Sep 7, 2009 8:03 UTC (Mon) by bvdm (guest, #42755) [Link] (1 responses)

You are a fortunate man to have the time and opportunity to traverse Silicon Valley so thoroughly :-p

But seriously, the only objective measures we have are the number of contributors and SLOC added, and both of these are still accelerating.

Now I would be astounded if the Linux kernel were the only technical project in the world without non-technical problems, but don't you think there are many other explanations for this change in perception? Such as, perhaps:

- That having your code included in the kernel has a much increased monetary benefit and is therefore more sought after
- That the existing kernel developers have increased in their experience and skill and that standards for acceptance are therefore higher today
- That the stature of being a core kernel developer has risen and that ego may be involved
- That many parts of the kernel is near-optimal or at least very mature and that it is sensible to value stability in those areas

And are the driver staging tree and desktop and security advances such as KMS and SMACK not countersigns to what you are suggesting?

Well, this settles it for me

Posted Sep 7, 2009 18:24 UTC (Mon) by k8to (guest, #15413) [Link]

It's not the money.

It's likely to be driven by standards, but the contention is that these standards are often more arbitrary than useful.

Ego on the part of the maintainers is certainly involved. Among my contacts, ego on the part of the author has certain not *risen* in the interim, although it may be high (I doubt it).

Stability has certainly become more prized.

Well, this settles it for me

Posted Sep 7, 2009 16:06 UTC (Mon) by einstein (subscriber, #2052) [Link] (1 responses)

> Firstly, Linux has a very small desktop presence,

I don't think that we desktop linux users are entirely happy with smug little comments like that. For us, linux is the only desktop presence and it looms large.

> so not entirely optimizing for the desktop is a rational design decision, though "totally disconnected" is very hard to swallow.

I think Con may have a valid point in questioning the one-size fits all paradigm. While it's an admirable goal to create a single kernel which runs optimally on everything from PDAs to supercomputing clusters, there may be too much of a divergence in performance profiles for that to be entirely practical.

As Linus has said, a desktop linux presence is vital to its viability, so optimizing desktop interactivity ought to be a very high priority.

Well, this settles it for me

Posted Sep 7, 2009 22:24 UTC (Mon) by mingo (subscriber, #31122) [Link]

As Linus has said, a desktop linux presence is vital to its viability, so optimizing desktop interactivity ought to be a very high priority.

It is. See for example this recent discussion on lkml. That discussion and those (non-trivial) patches were all about desktop latencies - and it's all part of v2.6.30 now.

Because I can

Posted Sep 7, 2009 22:20 UTC (Mon) by man_ls (guest, #15091) [Link] (4 responses)

As for netbooks, if interactivity (people keep posting about gaming FPS and high-def audio and high-res desktop experience) is such a concern, why are you using a netbook?

Because they are light and cute? You have not understood what "interactivity" means. People do not post about FPS or high-def audio per se, but about jitter, frame drops and audio skips. Those are really nasty when watching a movie or listening to music, and computers are said to be multitasking these days.

Because I can

Posted Sep 9, 2009 7:57 UTC (Wed) by gmaxwell (guest, #30048) [Link] (3 responses)

Jitter, frame drops, and audio skips are all *easily measurable*. Yet *none* of the advocacy of BFS that I've seen includes any measure of these things. Only vague hand-waving about smoothness. Perhaps these people should color the edges of there disks with green markers... I hear it reduces jitter.

Meanwhile I do audio processing with a ~2ms processing interval using the mainline scheduler, thrashing the system, high loads... and underruns are basically unheard of at least after tossing the drivers and hardware that I determined were misbehaving (with measurements, ... imagine that!)

I don't doubt that there are genuine areas for improvement, even in the scheduler but it isn't going to get better without real measurements and some social skills superior to those of Hans Reiser.

Interactive benchmarks

Posted Sep 9, 2009 20:14 UTC (Wed) by man_ls (guest, #15091) [Link] (2 responses)

You are right, there are no benchmarks that show that BFS is good at interactivity. However I contend that such "hand-waving" is to be expected from an anaesthetist and a crowd of enthusiasts (and is not a bad thing at all). The real pity is that on lkml, a list full of high-flying engineers, nobody has been able to construct those benchmarks or do those measurements either. The best we have is a scheduler hacker posting odd benchmarks on esoteric hardware. No offense for Ingo, he was very respectful and had interesting data, but it was all biased:

we tune the Linux scheduler for desktop and small-server workloads mostly [...] what i consider a sane range of systems to tune for - and should still fit into BFS's design bracket as well according to your description: it's a dual quad core system with hyperthreading

And then repeating the measures on a quad-core machine, the best he has offered so far. It seems that, despite having an expressed focus on the desktop, a netbook and a few days for testing on it are out of reach.

As to the benchmarks, the first test was how fast can he build the kernel using n processes. Well, this is only measuring thoughput; if each process is supposed to be interactive, it is not unreasonable to expect that they will more easily interrupted and thus the build will last longer. Then a very artificial pipe-messaging test, followed by similarly contrived benchmarks -- which CFS has already been tuned to. So the "other side" (lkml) has not been able to produce anything better either to show that CFS is good at interactivity, measuring skips and jitter, and I find this to be even more pitiful.

Interactive benchmarks

Posted Sep 9, 2009 23:40 UTC (Wed) by njs (subscriber, #40338) [Link] (1 responses)

> As to the benchmarks, the first test was how fast can he build the kernel using n processes.

To be fair, that benchmark is originally Con's, not Ingo's (Con's original announcement claims that "make -j4 on a quad core machine with BFS is faster than *any* choice of job numbers on CFS").

Interactive benchmarks

Posted Sep 10, 2009 9:52 UTC (Thu) by man_ls (guest, #15091) [Link]

More to the point: even when one side proposed invalid benchmarks, the other side was not able to come up with anything better. (And no, "beat them at their own benchmarks" is not a valid excuse; we are talking about engineering, not about marketing.)