Date: Sun, 21 Dec 2008 13:46:28 +0800 From: David Xu <davidxu@freebsd.org> To: Ravi Murty <ravi.murty@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: td_critnest Message-ID: <494DD834.7050108@freebsd.org> In-Reply-To: <95b10a340812142103u3ab8bd2br97033a7c7e8bec3@mail.gmail.com> References: <95b10a340812142103u3ab8bd2br97033a7c7e8bec3@mail.gmail.com>
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Ravi Murty wrote: > Hello All, > > The implementation of critical_enter and critical_exit changed between > freebsd 5 and freebsd 6. In the newer implemtnation, the code checks if > td_critnest is 1 and if it is sets it to zero, then checks if the thread > owes a preempt. If so, it increments td_critnest by 1 before grabbing a lock > and then decrements it back to zero. I can't figure out why it does this. > The freebsd 5 implementation seems straightforward where we check if the > thread owes a preempt and if so we switch to the new thread. Can anyone help > me with this? > > Thanks > Ravi I guess this becauses thread_lock() also calls critical_exit(), this code avoids recursion.
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