Date: Thu, 3 Jan 2013 15:44:52 -0500 From: John Baldwin <jhb@freebsd.org> To: Jim Harris <jim.harris@gmail.com> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r244549 - head/sys/dev/nvme Message-ID: <201301031544.52750.jhb@freebsd.org> In-Reply-To: <CAJP=Hc9PvmR5yUMH5=YvQ9e%2BtJ7j3PqtDHGebA8nvvTqB%2BX=xw@mail.gmail.com> References: <201212211913.qBLJDmpm019837@svn.freebsd.org> <201212211424.16934.jhb@freebsd.org> <CAJP=Hc9PvmR5yUMH5=YvQ9e%2BtJ7j3PqtDHGebA8nvvTqB%2BX=xw@mail.gmail.com>
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On Friday, December 21, 2012 04:49:13 PM Jim Harris wrote: > On Fri, Dec 21, 2012 at 12:24 PM, John Baldwin <jhb@freebsd.org> wrote: > > On Friday, December 21, 2012 2:13:48 pm Jim Harris wrote: > > > Author: jimharris > > > Date: Fri Dec 21 19:13:48 2012 > > > New Revision: 244549 > > > URL: http://svnweb.freebsd.org/changeset/base/244549 > > > > > > Log: > > > Put kthreads under curproc so they are attached to nvmecontrol rather > > > than pid 0. > > > > > > Sponsored by: Intel > > > > Hmm, is this really wise? I'm not sure how well the kernel would handle > > a kthread belonging to a userland process. You could just have each > > test create a new kproc that holds the associated threads for that test > > instead perhaps? > > Just so I'm aware, what sorts of problems might you expect if a kthread > belongs to a userland process? I'm not opposed to changing this as you > suggest, but would like to know for my own understanding since I haven't > observed any problems with it on my system. I'm not sure what might break. :( I just know that I have always expected a kthread to belong to a kernel process, and it wouldn't surprise me if there wasn't some code somewhere that assumed TDP_KTHREAD implied that the associated process as a kernel process (P_SYSTEM). Perhaps it would work, but I don't think many folks have considered that edge case or coded for it. OTOH, it might be an interesting way to implement aio (though I think aio should be implemented directly in userland using user threads, though possibly not pthreads so a single-threaded application doesn't pay a penalty). -- John Baldwin
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