Date: Fri, 02 Dec 2011 15:08:16 -0500 From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r228207 - head/sys/kern Message-ID: <4ED93030.6000203@FreeBSD.org> In-Reply-To: <201112021959.pB2Jxka6006739@svn.freebsd.org> References: <201112021959.pB2Jxka6006739@svn.freebsd.org>
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On 12/2/11 2:59 PM, John Baldwin wrote: > Author: jhb > Date: Fri Dec 2 19:59:46 2011 > New Revision: 228207 > URL: http://svn.freebsd.org/changeset/base/228207 > > Log: > When changing the user priority of a thread, change the real priority > in addition to the user priority for threads whose current real priority > is equal to the previous user priority or if the new priority is a > real-time priority. This allows priority changes of other threads to > have an immediate effect. An example that this fixes is suppose you have a CPU bound thread running on an dedicated CPU with rtprio and now want to run another quick thread on that CPU. The quick thread doesn't have rtprio and won't get a chance to run (by design). You want to fix this though so you lower the CPU bound thread to a lower rtprio and set the quick thread to rtprio 0. Without this fix the quick thread still won't get to run as the rtprio 0 will never take effect until the thread returns from userland. With this change it will now take effect immediately so the quick thread will preempt the CPU bound one. You can test this by scheduling two CPU bound rtprio threads on a single CPU (I used jot ${BIGNUM} >/dev/null) and frob the two processes relative realtime priorities. Before whatever jot started running first would never be preempted by the second jot, even if the second jot was assigned a higher RT priority. Now the the jot process with the highest RT priority always runs. -- John Baldwin
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