Date: Mon, 13 Jul 2009 15:05:04 -0400 From: John Baldwin <jhb@freebsd.org> To: "Robert N. M. Watson" <rwatson@freebsd.org> Cc: freebsd-hackers@freebsd.org, Sebastian Huber <sebastian.huber@embedded-brains.de> Subject: Re: callout(9) and Giant lock Message-ID: <200907131505.04688.jhb@freebsd.org> In-Reply-To: <732D77F4-6D18-4724-A76C-FB38B9DAE0F1@freebsd.org> References: <4A4740B8.8090205@embedded-brains.de> <200907131417.53876.jhb@freebsd.org> <732D77F4-6D18-4724-A76C-FB38B9DAE0F1@freebsd.org>
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On Monday 13 July 2009 2:49:24 pm Robert N. M. Watson wrote: > > On 13 Jul 2009, at 19:17, John Baldwin wrote: > > >> Callouts are marked as MPSAFE or non-MPSAFE when registered. If > >> non-MPSAFE, > >> we will acquire Giant automatically for the callout, but I believe > >> we'll also > >> try and sort non-MPSAFE callouts behind MPSAFE ones in execution > >> order to > >> minimize latency for MPSAFE callouts. Most callouts acquire locks > >> of some > >> sort, and stalling any callout indefinitely will stall the entire > >> callout > >> thread indefinitely, which in turn could lead to a variety of odd > >> behaviors > >> and potentially (although not necessarily) deadlock. > > > > FWIW, we do not actually sort the callouts in this manner, so all > > callouts > > will be blocked until Giant is acquired. > > I must have been remembering a proposed change -- as you say, it's > certainly not in kern_timeout.c. However, I'd rather just eliminate > support for Giant in callouts in 9.x than try to further facilitate > them :-) Agreed. :) -- John Baldwin
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