Messages in this thread Patch in this message | | | Date | Sat, 13 Apr 2024 18:29:20 +0800 | From | Dawei Li <> | Subject | Re: [PATCH 3/6] irqchip/gic-v3-its: Avoid explicit cpumask allocation on stack |
| |
Hi Marc,
Thanks for the review.
On Fri, Apr 12, 2024 at 02:53:32PM +0100, Marc Zyngier wrote: > On Fri, 12 Apr 2024 11:58:36 +0100, > Dawei Li <dawei.li@shingroup.cn> wrote: > > > > In general it's preferable to avoid placing cpumasks on the stack, as > > for large values of NR_CPUS these can consume significant amounts of > > stack space and make stack overflows more likely. > > > > Remove cpumask var on stack and use proper cpumask API to address it. > > Define proper. Or better, define what is "improper" about the current > usage.
Sorry for the confusion.
I didn't mean current implementation is 'improper', actually both implementations share equivalent API usages. I will remove this misleading expression from commit message.
> > > > > Signed-off-by: Dawei Li <dawei.li@shingroup.cn> > > --- > > drivers/irqchip/irq-gic-v3-its.c | 9 ++++++--- > > 1 file changed, 6 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c > > index fca888b36680..a821396c4261 100644 > > --- a/drivers/irqchip/irq-gic-v3-its.c > > +++ b/drivers/irqchip/irq-gic-v3-its.c > > @@ -3826,7 +3826,7 @@ static int its_vpe_set_affinity(struct irq_data *d, > > bool force) > > { > > struct its_vpe *vpe = irq_data_get_irq_chip_data(d); > > - struct cpumask common, *table_mask; > > + struct cpumask *table_mask; > > unsigned long flags; > > int from, cpu; > > > > @@ -3850,8 +3850,11 @@ static int its_vpe_set_affinity(struct irq_data *d, > > * If we are offered another CPU in the same GICv4.1 ITS > > * affinity, pick this one. Otherwise, any CPU will do. > > */ > > - if (table_mask && cpumask_and(&common, mask_val, table_mask)) > > - cpu = cpumask_test_cpu(from, &common) ? from : cpumask_first(&common); > > + if (table_mask && cpumask_intersects(mask_val, table_mask)) { > > + cpu = cpumask_test_cpu(from, mask_val) && > > + cpumask_test_cpu(from, table_mask) ? > > + from : cpumask_first_and(mask_val, table_mask); > > So we may end-up computing the AND of the two bitmaps twice (once for > cpumask_intersects(), once for cpumask_first_and()), instead of only > doing it once.
Actually maybe it's possible to merge these 2 bitmap ops into one:
diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c index fca888b36680..7a267777bd0b 100644 --- a/drivers/irqchip/irq-gic-v3-its.c +++ b/drivers/irqchip/irq-gic-v3-its.c @@ -3826,7 +3826,8 @@ static int its_vpe_set_affinity(struct irq_data *d, bool force) { struct its_vpe *vpe = irq_data_get_irq_chip_data(d); - struct cpumask common, *table_mask; + struct cpumask *table_mask; + unsigned int common; unsigned long flags; int from, cpu;
@@ -3850,10 +3851,13 @@ static int its_vpe_set_affinity(struct irq_data *d, * If we are offered another CPU in the same GICv4.1 ITS * affinity, pick this one. Otherwise, any CPU will do. */ - if (table_mask && cpumask_and(&common, mask_val, table_mask)) - cpu = cpumask_test_cpu(from, &common) ? from : cpumask_first(&common); - else + if (table_mask && (common = cpumask_first_and(mask_val, table_mask)) < nr_cpu_ids) { + cpu = cpumask_test_cpu(from, mask_val) && + cpumask_test_cpu(from, table_mask) ? + from : common; + } else { cpu = cpumask_first(mask_val); + }
> > I don't expect that to be horrible, but I also note that you don't > even talk about the trade-offs you are choosing to make.
With change above, I assume that the tradeoff is minor and can be ignored?
And I aplogize if I am missing something. > > > + } > > else > > cpu = cpumask_first(mask_val); > > Please fix the coding style (if () { ... } else { ... }).
Ack.
Thanks,
Dawei
> > M. > > -- > Without deviation from the norm, progress is not possible. >
| |