Date: Thu, 1 Apr 2010 13:10:14 GMT From: John Baldwin <jhb@freebsd.org> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/117954: [ufs] dirhash on very large directories blocks the machine for tens of seconds Message-ID: <201004011310.o31DAEHT000127@freefall.freebsd.org>
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The following reply was made to PR kern/117954; it has been noted by GNATS. From: John Baldwin <jhb@freebsd.org> To: bug-followup@freebsd.org, martin@nowhere.com Cc: Subject: Re: kern/117954: [ufs] dirhash on very large directories blocks the machine for tens of seconds Date: Thu, 1 Apr 2010 09:01:57 -0400 While the kernel scheduler will not preempt a thread in the kernel (e.g. during a system call) if a timeslice expires, it will preempt that thread for interrupts (assuming you have 'options PREEMPTION' enabled which has been on by default in GENERIC for some time now on i386), thus the dirhash calculations should not starve interrupts. However, X is not an interrupt, so while things like ping should still work, X will not get to run. While it would be tempting to defer the hashing of the directory contents to an asynchronous task for large directories running in a thread with a low priority, this might have bad side effects due to priority inversions related to a very low priority thread holding various vnode locks. -- John Baldwin
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