Date: Thu, 3 Feb 2011 07:50:06 -0500 From: John Baldwin <jhb@freebsd.org> To: Juli Mallett <jmallett@freebsd.org> Cc: svn-src-head@freebsd.org, Matthew D Fleming <mdf@freebsd.org>, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r218195 - in head/sys: amd64/amd64 arm/arm i386/i386 ia64/ia64 kern mips/mips powerpc/powerpc sparc64/sparc64 sun4v/sun4v sys ufs/ffs Message-ID: <201102030750.07076.jhb@freebsd.org> In-Reply-To: <AANLkTi=5jDcYAfuoWtgDTUk__JJK222efBd9YgPq6hsf@mail.gmail.com> References: <201102021635.p12GZA94015170@svn.freebsd.org> <AANLkTi=5jDcYAfuoWtgDTUk__JJK222efBd9YgPq6hsf@mail.gmail.com>
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On Thursday, February 03, 2011 2:47:20 am Juli Mallett wrote: > On Wed, Feb 2, 2011 at 08:35, Matthew D Fleming <mdf@freebsd.org> wrote: > > Author: mdf > > Date: Wed Feb 2 16:35:10 2011 > > New Revision: 218195 > > URL: http://svn.freebsd.org/changeset/base/218195 > > > > Log: > > Put the general logic for being a CPU hog into a new function > > should_yield(). Use this in various places. Encapsulate the common > > case of check-and-yield into a new function maybe_yield(). > > > > Change several checks for a magic number of iterations to use > > should_yield() instead. > > First off, I admittedly don't know or care very much about this area, > but this commit stood out to me and I had a few minor concerns. > > I'm slightly uncomfortable with the flat namespace here. It isn't > obvious from the names that maybe_yield() and should_yield() relate > only to uio_yield() and not other types of yielding (from DELAY() to > cpu_idle() to sched_yield().) The other problematic element here is > that "maybe_yield" and "should_yield" could quite reasonably be > variables or functions in existing code in the kernel, and although we > don't try to protect against changes that could cause such collisions, > we shouldn't do them gratuitously, and there's even something that > seems aesthetically off about these; they seem...informal, even > Linuxy. I think names like uio_should_yield() and uio_maybe_yield() > wouldn't have nearly as much of a problem, since the context of the > question of "should" is isolated to uio operations rather than, say, > whether the scheduler would *like* for us, as the running thread, to > yield, or other considerations that may be more general. I mostly agree, but these checks are no longer specific to uio. Matt used them to replace many ad-hoc checks using counters with hardcoded maximums in places like softupdates, etc. I don't have any good suggestions for what else you would call these. I'm not sure 'sched_amcpuhog() or sched_hoggingcpu()' are really better (and these are not scheduler dependent, so sched_ would probably not be a good prefix). -- John Baldwin
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