On 09/26/2012 11:08 PM, Chuansheng Liu wrote:
>
> When one CPU is going offline, and fixup_irqs() will re-set the
> irq affinity in some cases, we should clean the offlining CPU from
> the irq affinity.
>
> The reason is setting offlining CPU as of the affinity is useless.
> Moreover, the smp_affinity value will be confusing when the
> offlining CPU come back again.
>
> Example:
> For irq 93 with 4 CPUS, the default affinity f(1111),
> normal cases: 4 CPUS will receive the irq93 interrupts.
>
> When echo 0 > /sys/devices/system/cpu/cpu3/online, just CPU0,1,2 will
> receive the interrupts.
>
> But after the CPU3 is online again, we will not set affinity,the result
> will be:
> the smp_affinity is f, but still just CPU0,1,2 can receive the interrupts.
>
> So we should clean the offlining CPU from irq affinity mask
> in fixup_irqs().
>
> Reviewed-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
Please hold on.. I'm not yet done reviewing, I might have more comments :-)
> Signed-off-by: liu chuansheng <chuansheng....@intel.com>
> ---
> arch/x86/kernel/irq.c | 8 ++++++--
> 1 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
> index d44f782..08bb905 100644
> --- a/arch/x86/kernel/irq.c
> +++ b/arch/x86/kernel/irq.c
> @@ -239,6 +239,7 @@ void fixup_irqs(void)
> struct irq_desc *desc;
> struct irq_data *data;
> struct irq_chip *chip;
> + int cpu = smp_processor_id();
>
> for_each_irq_desc(irq, desc) {
> int break_affinity = 0;
> @@ -277,8 +278,11 @@ void fixup_irqs(void)
> if (!irqd_can_move_in_process_context(data) && chip->irq_mask)
> chip->irq_mask(data);
>
> - if (chip->irq_set_affinity)
> - chip->irq_set_affinity(data, affinity, true);
> + if ((chip->irq_set_affinity) &&
> + !chip->irq_set_affinity(data, affinity, true)) {
A return value of 0 and 1 are acceptable. So this check isn't correct.
Regards,
Srivatsa S. Bhat
> + if (cpumask_test_cpu(cpu, data->affinity))
> + cpumask_clear_cpu(cpu, data->affinity);
OMG, why did you drop the other hunk which cleared the cpu *before*
invoking ->irq_set_affinity()? IMO, altering irq affinity involves more work
than just altering the mask; that's why you have that ->irq_set_affinity()
function. So, if you alter the mask *after* calling ->irq_set_affinity(),
its not right..
Regards,
Srivatsa S. Bhat
> + }
> else if (!(warned++))
> set_affinity = 0;
>
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