From owner-freebsd-smp  Fri Aug 31 10:35:31 2001
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Date: Fri, 31 Aug 2001 10:50:28 -0700 (PDT)
From: Julian Elischer <julian@elischer.org>
To: Tor.Egge@fast.no
Cc: mb@imp.ch, bde@zeta.org.au, bkarp@icsi.berkeley.edu,
	kpielorz@tdx.co.uk, sthaug@nethelp.no, atrn@zeta.org.au,
	roberto@eurocontrol.fr, drussell@saturn-tech.com, phk@FreeBSD.ORG,
	Patrick.Guelat@imp.ch, freebsd-hackers@FreeBSD.ORG,
	freebsd-smp@FreeBSD.ORG
Subject: Re: Clock speedup on 4.X FreeBSD SMP and serverworks chipset
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tor, will you commit this?


On Fri, 31 Aug 2001 Tor.Egge@fast.no wrote:

> 
> I wrote:
> 
> > The problem here is that CPU#1 fails to hold clock_lock while setting
> > clkintr_pending, causing i8254_offset to be stepped twice, first due
> > to clkintr_pending, then due to i8254_lastcount being larger than count.
> 
> With this patch applied to RELENG_4, the clock speedup seems to disappear.
> 
> 
> --- apic_vector.s.old	Fri Mar  2 13:47:31 2001
> +++ apic_vector.s	Fri Aug 31 01:07:53 2001
> @@ -707,7 +707,12 @@
>  	FAST_INTR(21,fastintr21)
>  	FAST_INTR(22,fastintr22)
>  	FAST_INTR(23,fastintr23)
> -#define	CLKINTR_PENDING	movl $1,CNAME(clkintr_pending)
> +#define	CLKINTR_PENDING	pushl $clock_lock;		\
> +			call s_lock;			\
> +			movl $1,CNAME(clkintr_pending);	\
> +			call s_unlock;			\
> +			addl $4, %esp
> +
>  	INTR(0,intr0, CLKINTR_PENDING)
>  	INTR(1,intr1,)
>  	INTR(2,intr2,)
> 
> 
> The corresponding patch for -current is
> 
> Index: apic_vector.s
> ===================================================================
> RCS file: /home/ncvs/src/sys/i386/isa/apic_vector.s,v
> retrieving revision 1.71
> diff -u -r1.71 apic_vector.s
> --- apic_vector.s	27 Apr 2001 19:28:21 -0000	1.71
> +++ apic_vector.s	31 Aug 2001 01:35:05 -0000
> @@ -7,6 +7,8 @@
>  #include <machine/apic.h>
>  #include <machine/smp.h>
>  
> +#include <machine/mutex.h>
> +
>  #include "i386/isa/intr_machdep.h"
>  
>  /* convert an absolute IRQ# into a bitmask */
> @@ -384,7 +425,11 @@
>  	FAST_INTR(29,fastintr29)
>  	FAST_INTR(30,fastintr30)
>  	FAST_INTR(31,fastintr31)
> -#define	CLKINTR_PENDING	movl $1,CNAME(clkintr_pending)
> +#define	CLKINTR_PENDING	MTX_LOCK_SPIN(clock_lock, 0); \
> +			movl $1,CNAME(clkintr_pending);	\
> +			MTX_UNLOCK_SPIN(clock_lock)
> +
> +	
>  /* Threaded interrupts */
>  	INTR(0,intr0, CLKINTR_PENDING)
>  	INTR(1,intr1,)
> 
> 
> - Tor Egge
> 
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