Jan Beulich
2010-Jul-07 08:50 UTC
[Xen-devel] [PATCH, RFC] x86: eliminate bogus IRQ restrictions
As pointed out in
http://lists.xensource.com/archives/html/xen-devel/2010-07/msg00077.html
the limits introduced in c/s 20072 are at least questionable. Eliminate
them in favor of a more dynamic approach: There''s no real need for an
upper limit on nr_irqs (as anything beyond nr_irqs_gsi isn#t visible to
domains anyway), and the split point (and hence ratio) between GSI and
MSI/MSI-X IRQs doesn''t need to be hard coded, but can instead be
controlled on the command line in case there are *very* many GSIs.
The default used for nr_irqs will be rather large with this patch, so
it may not be acceptable without also switching to a sparse irq_desc[]
as was done not so lomg ago in Linux.
The added capping of any domain''s nr_pirqs is based on the observation
that no domain can possibly have more than the system wide number of
IRQs. The opposite case may in fact also require some adjustment:
Defaulting the number of non-GSI IRQs available (namely to Dom0) to a
fixed value may not be the best choice going forward, since if there
indeed are very many non-GSI interrupt sources, it won''t be possible
for the kernel to make use of them without giving "extra_guest_irqs="
on the command line (but the goal should be to allow things to work
right by default even on large systems).
Signed-off-by: Jan Beulich <jbeulich@novell.com>
--- 2010-06-15.orig/xen/arch/x86/io_apic.c 2010-07-06 16:12:49.000000000 +0200
+++ 2010-06-15/xen/arch/x86/io_apic.c 2010-07-07 09:21:57.000000000 +0200
@@ -2385,6 +2385,9 @@ void dump_ioapic_irq_info(void)
unsigned highest_gsi(void);
+static unsigned int __initdata max_gsi_irqs;
+integer_param("max_gsi_irqs", max_gsi_irqs);
+
void __init init_ioapic_mappings(void)
{
unsigned long ioapic_phys;
@@ -2429,19 +2432,37 @@ void __init init_ioapic_mappings(void)
nr_irqs_gsi = max(nr_irqs_gsi, highest_gsi());
+ if ( max_gsi_irqs == 0 )
+ max_gsi_irqs = nr_irqs ? nr_irqs / 8 : PAGE_SIZE;
+ else if ( nr_irqs != 0 && max_gsi_irqs > nr_irqs )
+ {
+ printk(XENLOG_WARNING "\"max_gsi_irqs=\" cannot be
specified larger"
+ " than \"nr_irqs=\"\n");
+ max_gsi_irqs = nr_irqs;
+ }
+ if ( max_gsi_irqs < 16 )
+ max_gsi_irqs = 16;
+
+ /* for PHYSDEVOP_pirq_eoi_gmfn guest assumptions */
+ if ( max_gsi_irqs > PAGE_SIZE * 8 )
+ max_gsi_irqs = PAGE_SIZE * 8;
+
if ( !smp_found_config || skip_ioapic_setup || nr_irqs_gsi < 16 )
nr_irqs_gsi = 16;
- else if ( nr_irqs_gsi > MAX_GSI_IRQS)
+ else if ( nr_irqs_gsi > max_gsi_irqs )
{
- /* for PHYSDEVOP_pirq_eoi_gmfn guest assumptions */
- printk(KERN_WARNING "Limiting number of GSI IRQs found (%u) to
%lu\n",
- nr_irqs_gsi, MAX_GSI_IRQS);
- nr_irqs_gsi = MAX_GSI_IRQS;
+ printk(XENLOG_WARNING "Limiting to %u GSI IRQs (found %u)\n",
+ max_gsi_irqs, nr_irqs_gsi);
+ nr_irqs_gsi = max_gsi_irqs;
}
- if (nr_irqs < 2 * nr_irqs_gsi)
- nr_irqs = 2 * nr_irqs_gsi;
-
- if (nr_irqs > MAX_NR_IRQS)
- nr_irqs = MAX_NR_IRQS;
+ if ( nr_irqs == 0 )
+ nr_irqs = cpu_has_apic ?
+ max(16U + num_present_cpus() * NR_DYNAMIC_VECTORS,
+ 8 * nr_irqs_gsi) :
+ nr_irqs_gsi;
+ else if ( nr_irqs < 16 )
+ nr_irqs = 16;
+ printk(XENLOG_INFO "IRQ limits: %u GSI, %u MSI/MSI-X\n",
+ nr_irqs_gsi, nr_irqs - nr_irqs_gsi);
}
--- 2010-06-15.orig/xen/arch/x86/irq.c 2010-06-29 10:15:13.000000000 +0200
+++ 2010-06-15/xen/arch/x86/irq.c 2010-07-07 08:34:59.000000000 +0200
@@ -29,7 +29,7 @@ int __read_mostly opt_noirqbalance = 0;
boolean_param("noirqbalance", opt_noirqbalance);
unsigned int __read_mostly nr_irqs_gsi = 16;
-unsigned int __read_mostly nr_irqs = 1024;
+unsigned int __read_mostly nr_irqs;
integer_param("nr_irqs", nr_irqs);
u8 __read_mostly *irq_vector;
--- 2010-06-15.orig/xen/common/domain.c 2010-06-11 11:41:35.000000000 +0200
+++ 2010-06-15/xen/common/domain.c 2010-07-07 09:42:43.000000000 +0200
@@ -270,6 +270,8 @@ struct domain *domain_create(
d->nr_pirqs = nr_irqs_gsi + extra_domU_irqs;
else
d->nr_pirqs = nr_irqs_gsi + extra_dom0_irqs;
+ if ( d->nr_pirqs > nr_irqs )
+ d->nr_pirqs = nr_irqs;
d->pirq_to_evtchn = xmalloc_array(u16, d->nr_pirqs);
d->pirq_mask = xmalloc_array(
--- 2010-06-15.orig/xen/include/asm-x86/irq.h 2010-06-15 09:21:05.000000000
+0200
+++ 2010-06-15/xen/include/asm-x86/irq.h 2010-07-07 08:32:10.000000000 +0200
@@ -23,9 +23,6 @@
#define irq_to_desc(irq) (&irq_desc[irq])
#define irq_cfg(irq) (&irq_cfg[irq])
-#define MAX_GSI_IRQS PAGE_SIZE * 8
-#define MAX_NR_IRQS (2 * MAX_GSI_IRQS)
-
struct irq_cfg {
int vector;
cpumask_t domain;
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