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Re: Making spl7 just cli/sti?

From: Richard Braun
Subject: Re: Making spl7 just cli/sti?
Date: Sun, 14 Dec 2014 15:44:44 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

On Sun, Dec 14, 2014 at 02:44:08AM +0100, Samuel Thibault wrote:
> Does anybody with a bit of background with spl (I guess Richard?) see
> any red flag here?

No, and in fact, I don't like the idea of SPL/IPL. For example, Linux
doesn't care about them and merely disables or enables interrupts at
the processor level, the semantics being all or nothing, and it shows
it works quite well.

An IPL (interrupt priority level) is basically a system of
not-so-coarsed-grained locking. The spl (set priority level) functions
act as lock/unlock primitives. In that regard, using cli/sti is
equivalent to acquiring/releasing a big kernel lock. If the critical
sections protected by this lock are all small enough, granularity
tends to matter much less. My point being that this could be generalized
for all IPLs, since they are all affected by the virtualization penalty.

Richard Braun

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