Date: Thu, 01 Jan 2015 13:36:31 +0100 From: Hans Petter Selasky <hps@selasky.org> To: Ivan Klymenko <fidaj@ukr.net> Cc: FreeBSD Current <freebsd-current@freebsd.org>, freebsd-arch@freebsd.org Subject: Re: [RFC] kern/kern_timeout.c rewrite in progress Message-ID: <54A53F4F.2000003@selasky.org> In-Reply-To: <54A4A002.8010802@selasky.org> References: <54A1B38C.1000709@selasky.org> <20150101005613.4f788b0c@nonamehost.local> <54A49CA5.2060801@selasky.org> <54A4A002.8010802@selasky.org>
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On 01/01/15 02:16, Hans Petter Selasky wrote: > On 01/01/15 02:02, Hans Petter Selasky wrote: >> On 12/31/14 23:56, Ivan Klymenko wrote: >>> В Mon, 29 Dec 2014 21:03:24 +0100 >>> Hans Petter Selasky <hps@selasky.org> пишет: >>> >> >> Hi, >> >> Is your kernel compiled with Witness? Do you see any lock order reversal >> warnings? >> >> Can you do from kgdb: >> >> thread apply all bt >> >> And send me the result off-list? >> >> I'll have a closer look at this tomorrow. >> >>> >>> panic: spin lock held too long >>> http://paste.org.ru/?acf7io >>> >> >> Thank you! >> > Hi, I see what is going on. There is an LOR which is not printed because MTX_QUIET is passed when locking inside the callback process routine. It happens because cv_timedwait() is using callouts() to timeout and callout_drain() is using cv_wait() to wait for draining. This was not so well documented in the old code. I'll update my patch and send out a new one later today. I see a room for doing some improvements too: callout_init(&td->td_slpcallout, CALLOUT_MPSAFE) Possibly we could use a so-called "DIRECT" callback from the fast IRQ of the timer, when waking up other threads from cv_timedwait(), hence only spinlocks are involved? This would save waking up the callout SWI only to wakeup another thread ! Thank you for testing! --HPS
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