Messages in this thread | | | From | James Cleverdon <> | Subject | Re: [PATCH] 2.5.17 fix for running a SMP kernel on a UP box | Date | Tue, 21 May 2002 19:36:39 -0700 |
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I was looking at this with Jack Vogel and I can't figure out how it goes wrong, either. However, the code in move() that uses the cpu number is a bit strange. Entering loops in their middles is generally considered bug-prone by programming style books. What about eliminating the goto by using something like the attached patch?
On Tuesday 21 May 2002 02:52 pm, Greg KH wrote: > I can't seem to run a SMP 2.5.17 kernel on a UP machine, it locks up > during the boot process. In talking to Jack Vogel, he suggested I make > the following patch, which seems to solve the problem for me. In > looking at the code, I have no idea of why this seems to work, so there > probably is a better fix out there. > > Any suggestions? > > thanks, > > greg k-h > > > > diff -Nru a/arch/i386/kernel/io_apic.c b/arch/i386/kernel/io_apic.c > --- a/arch/i386/kernel/io_apic.c Tue May 21 14:47:06 2002 > +++ b/arch/i386/kernel/io_apic.c Tue May 21 14:47:06 2002 > @@ -205,7 +205,7 @@ > } ____cacheline_aligned irq_balance_t; > > static irq_balance_t irq_balance[NR_IRQS] __cacheline_aligned > - = { [ 0 ... NR_IRQS-1 ] = { 1, 0 } }; > + = { [ 0 ... NR_IRQS-1 ] = { 0, 0 } }; > > extern unsigned long irq_affinity [NR_IRQS]; > > -
-- James Cleverdon IBM xSeries Linux Solutions {jamesclv(Unix, preferred), cleverdj(Notes)} at us dot ibm dot com *** linux/arch/i386/kernel/io_apic.c.df Mon May 20 22:07:36 2002 --- linux/arch/i386/kernel/io_apic.c Tue May 21 18:41:54 2002 *************** *** 203,213 **** unsigned int cpu; unsigned long timestamp; } ____cacheline_aligned irq_balance_t; static irq_balance_t irq_balance[NR_IRQS] __cacheline_aligned ! = { [ 0 ... NR_IRQS-1 ] = { 1, 0 } }; extern unsigned long irq_affinity [NR_IRQS]; #endif --- 203,213 ---- unsigned int cpu; unsigned long timestamp; } ____cacheline_aligned irq_balance_t; static irq_balance_t irq_balance[NR_IRQS] __cacheline_aligned ! = { [ 0 ... NR_IRQS-1 ] = { 0, 0 } }; extern unsigned long irq_affinity [NR_IRQS]; #endif *************** *** 220,248 **** static unsigned long move(int curr_cpu, unsigned long allowed_mask, unsigned long now, int direction) { int search_idle = 1; int cpu = curr_cpu; ! goto inside; ! ! do { ! if (unlikely(cpu == curr_cpu)) ! search_idle = 0; ! inside: ! if (direction == 1) { ! cpu++; ! if (cpu >= smp_num_cpus) cpu = 0; } else { ! cpu--; ! if (cpu == -1) ! cpu = smp_num_cpus-1; } ! } while (!IRQ_ALLOWED(cpu,allowed_mask) || ! (search_idle && !IDLE_ENOUGH(cpu,now))); ! ! return cpu; } static inline void balance_irq(int irq) { #if CONFIG_SMP --- 220,242 ---- static unsigned long move(int curr_cpu, unsigned long allowed_mask, unsigned long now, int direction) { int search_idle = 1; int cpu = curr_cpu; ! for (;;) { ! if (direction) { ! if (++cpu >= smp_num_cpus) cpu = 0; } else { ! if (--cpu < 0) ! cpu = smp_num_cpus - 1; } ! if (IRQ_ALLOWED(cpu, allowed_mask) && (!search_idle || IDLE_ENOUGH(cpu, now))) ! return cpu; ! if (unlikely(cpu == curr_cpu)) ! search_idle = 0; ! } } static inline void balance_irq(int irq) { #if CONFIG_SMP
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