From: Russ Cox <rsc@swtch.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Subject: Re: [9fans] kenfs question?
Date: Sat, 6 Feb 2010 16:12:07 -0800 [thread overview]
Message-ID: <dd6fe68a1002061612u754bf41ic04fbcfa2c2f2b4b@mail.gmail.com> (raw)
In-Reply-To: <20100206161207.GA31545@centaur.acm.jhu.edu>
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>
> ilock() (pc/lock.c) calls splhi() and then calls lock(). If that lock were
> contended, how would the system not stop? And on a UP system, if you're
> inside an splhi() block,
> why would you need to take an uncontended lock?
>
ilock is for locks that get used both in normal procs
and in interrupt handlers. Using splhi makes sure
that the interrupt handler does not get started on the
same cpu while the proc holds the lock, which would
cause a deadlock.
If there were no interrupts involved, the lock would be
managed with lock/unlock instead of ilock/iunlock.
On a uniprocessor you could get away with splhi/splx
instead of ilock/iunlock, but it's easier and more portable
to program as if always on a multiprocessor.
Russ
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next prev parent reply other threads:[~2010-02-07 0:12 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-06 16:12 Venkatesh Srinivas
2010-02-06 16:16 ` erik quanstrom
2010-02-11 13:31 ` Venkatesh Srinivas
2010-02-11 14:55 ` erik quanstrom
2010-02-07 0:12 ` Russ Cox [this message]
2010-02-07 3:02 ` Venkatesh Srinivas
2010-02-07 4:44 ` erik quanstrom
2010-02-07 10:42 ` Charles Forsyth
2010-02-07 12:19 ` Venkatesh Srinivas
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