pluggable I/O schedulers, pluggable CPU schedulers

Posted Jul 25, 2007 19:55 UTC (Wed) by mingo (guest, #31122)
In reply to: pluggable I/O schedulers, pluggable CPU schedulers by flewellyn
Parent article: Interview with Con Kolivas (APC)

Would it be possible to merge the I/O schedulers into one, and then expose the different behaviors as config knobs? Y'know, with "AS" and "CFQ" as particular groups of settings? Or is that just as bad if not worse?

You suggestion makes sense and i think it would likely result in fundamentally better code that gives us one codebase, but it still doesnt give us an IO scheduler that does the right thing no matter what we throw at it (the user would still have to turn that knob). So in that sense it would be little change from the current state of affairs.

The problem is not primarily the kernel-internal code duplication - we can handle such things pretty well, the kernel's nearly 8 million lines of code now and growing fast. We've got 3 SLAB implementations and that's not a problem because it was never made user (and application) visible.

The problem is the externally visible imperfection of the kernel's behavior, and when end-users learn to depend on it. If we try to remove such a knob we promised to users at a stage, those who are affected negatively complain (and rightfully so).

It should also be seen in perspective: these issues are not the end of the world, our I/O schedulers are pretty damn good already, and modularity is not an issue at all compared to some other kernel problems we are facing - but if code is submitted to an otherwise well-working subsystem these little factors are what make or break a particular patch's upstream acceptance.