Date: Fri, 23 Aug 2013 12:58:50 -0400 From: John Baldwin <jhb@freebsd.org> To: Davide Italiano <davide@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r254703 - in head: share/man/man9 sys/sys Message-ID: <201308231258.50969.jhb@freebsd.org> In-Reply-To: <CACYV=-H_CaCf9Ob=XW1fPZtPwNSYfdVdn2eNxnEV-ta7HiNhUw@mail.gmail.com> References: <201308231412.r7NECdG7081565@svn.freebsd.org> <201308231051.08997.jhb@freebsd.org> <CACYV=-H_CaCf9Ob=XW1fPZtPwNSYfdVdn2eNxnEV-ta7HiNhUw@mail.gmail.com>
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On Friday, August 23, 2013 11:29:45 am Davide Italiano wrote: > On Fri, Aug 23, 2013 at 4:51 PM, John Baldwin <jhb@freebsd.org> wrote: > > On Friday, August 23, 2013 10:12:39 am Davide Italiano wrote: > >> Author: davide > >> Date: Fri Aug 23 14:12:39 2013 > >> New Revision: 254703 > >> URL: http://svnweb.freebsd.org/changeset/base/254703 > >> > >> Log: > >> Introduce callout_init_rm() so that callouts can be used in conjunction > >> with rmlocks. This works only with non-sleepable rm because handlers run > >> in SWI context. While here, document the new KPI in the timeout(9) > >> manpage. > > > > It also only works with exclusive locks. (lc_unlock/lc_lock only handle > > write locks for rmlocks). > > > > -- > > John Baldwin > > Thanks for pointing out this. > I think it would be nice to have lc_lock/lc_unlock working both for > shared and exclusive locks but I'm not 100% sure about all the > implications/complications. From what I see for rwlocks asserting if a > lock is held in read-mode is really cheap (check against a flag) while > for rmlocks the assertion relies on traversing the tracker list for > the rmlock so I'm worried this operation could be expensive. What's > your opinion about? The much bigger problem is you need an rmtracker object to pass to the lock/unlock routines. You could make this work hackishly in the callout case by special casing rm locks that use read locking and using a tracker on softclock's stack, but it is much harder to fix this for the rm_sleep() case where the sequence is lc_unlock/lc_lock. -- John Baldwin
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