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Re: time.c CP0_COMPARE (and SMP IPI rambling)

To: Jun Sun <>
Subject: Re: time.c CP0_COMPARE (and SMP IPI rambling)
From: "Maciej W. Rozycki" <>
Date: Wed, 4 Sep 2002 12:50:25 +0200 (MET DST)
Cc: Ralf Baechle <>, Matthew Dharm <>, Linux-MIPS <>
In-reply-to: <>
Organization: Technical University of Gdansk
Original-recipient: rfc822;
On Tue, 3 Sep 2002, Jun Sun wrote:

> Right now setting per-cpu timers is totally left to the board-dependent code. 
>   Once we see more SMP boxes using this approach, I think it starts to be 
> interesting to make some abstraction and support it in a systematic way, 
> including support for using CPU counter as the per-cpu timer interrupt.
> Using local_timer_emulation sounds like an attractive alternative to me, as 
> we 
> only need to set up one system-wide timer interrupt.  Conceptually it 
> probably 
> takes a little longer to run through timer_interrupt (due to IPI calls).  But 
> if the hit on performance is very negligible, the simplicity might make it 
> worthwile.

 Well, the i386 approach (with a grain of salt, of course, but it's about
the most mature, anyway) seems reasonable.  A per-CPU local timer for
scheduling (no need to stability or high precision) and an external timer
interrupt for timekeeping (this one precise) that's delivered to a single
CPU at a time.  I hope there are no MIPS SMP systems that lack an external
timer IRQ source. 

+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+        e-mail:, PGP key available        +

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