On Fri, Aug 23, 2013 at 9:58 AM, John Baldwin <j...@freebsd.org> wrote: > On Friday, August 23, 2013 11:29:45 am Davide Italiano wrote: >> On Fri, Aug 23, 2013 at 4:51 PM, John Baldwin <j...@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
I see. I would really like to go for a clean solution if possible, and if the timeframe for 10 doesn't allow this just revert the commit until a better solution would be available. FWIW, I pondered a bit about this and the only way I was able to think is that of augmenting 'struct lock_object' with a 'void *arg' field that in this case could be used to store a pointer to something, which in this case is a pointer to a rmtracker object, and this could allow easily to retrieve the needed information (as far as I see something similar is done to store WITNESS information). This, OTOH, could be overkill just to fix this case though. Thanks, -- Davide "There are no solved problems; there are only problems that are more or less solved" -- Henri Poincare _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
