Date: Tue, 10 Aug 2004 09:18:45 -0400 From: John Baldwin <jhb@FreeBSD.org> To: Jeff Roberson <jeff@FreeBSD.org> Cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/kern sched_ule.c Message-ID: <200408100918.45387.jhb@FreeBSD.org> In-Reply-To: <200408100752.i7A7qMYI000506@repoman.freebsd.org> References: <200408100752.i7A7qMYI000506@repoman.freebsd.org>
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On Tuesday 10 August 2004 03:52 am, Jeff Roberson wrote: > jeff 2004-08-10 07:52:22 UTC > > FreeBSD src repository > > Modified files: > sys/kern sched_ule.c > Log: > - Use a new flag, KEF_XFERABLE, to record with certainty that this kse > had contributed to the transferable load count. This prevents any > potential problems with sched_pin() being used around calls to > setrunqueue(). - Change the sched_add() load balancing algorithm to try to > migrate on wakeup. This attempts to place threads that communicate with > each other on the same CPU. > - Don't clear the idle counts in kseq_transfer(), let the cpus do that > when they call sched_add() from kseq_assign(). > - Correct a few out of date comments. > - Make sure the ke_cpu field is correct when we preempt. > - Call kseq_assign() from sched_clock() to catch any assignments that > were done without IPI. Presently all assignments are done with an IPI, but > I'm trying a patch that limits that. > - Don't migrate a thread if it is still runnable in sched_add(). > Previously, this could only happen for KSE threads, but due to changes to > sched_switch() all threads went through this path. > - Remove some code that was added with preemption but is not necessary. Couple of comments: 1) TDF_NEEDRESCHED is still needed as that is what manages user-level preemptions. Kernel preemption does not normally preempt threads at user-level priorities (see the code in maybe_preempt() for a comment with more detailed info). 2) Can a thread bound to CPU B ever be put on the runqueue via setrunqueue() by a thread on CPU A? If so, you need to keep the SMP-specific migration check before the call to maybe_preempt() so that you don't end up running the new thread on CPU A even though it is supposed to run on CPU B. -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org
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