linux-kernel - Re: [PATCH 00/53] dyn_array/nr_irqs/sparse

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Date:	Thu, 14 Aug 2008 17:11:31 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Yinghai Lu" <yhlu.kernel@...il.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	"Alan Cox" <alan@...rguk.ukuu.org.uk>,
	"Andrew Morton" <akpm@...ux-foundation.org>
Subject: Re: [PATCH 00/53] dyn_array/nr_irqs/sparse_irq support v10

"Yinghai Lu" <yhlu.kernel@...il.com> writes:

> find something interesting:
>
> found new irq_cfg for irq 20
>  0 add_pin_to_irq: irq 20 --> apic 0 pin 20
> assign_irq_vector: irq 20 vector 0x59 cpu  5
> IOAPIC[0]: Set routing entry (0-20 -> 0x59 -> IRQ 20 Mode:1 Active:1)
> found new irq_desc for irq 20
> pci 0000:00:02.1: PCI INT B -> Link[LUS2] -> GSI 20 (level, low) -> IRQ 20
>
> IO APIC #0......
> .... register #00: 00000000
> .......    : physical APIC id: 00
> .......    : Delivery Type: 0
> .......    : LTS          : 0
> .... register #01: 00170011
> .......     : max redirection entries: 0017
> .......     : PRQ implemented: 0
> .......     : IO APIC version: 0011
> .... register #02: 00000000
> .......     : arbitration: 00
> .... IRQ redirection table:
>  NR Dst Mask Trig IRR Pol Stat Dmod Deli Vect:
> ...
>  14 09  1    1    0   1   0    0    0    59
> ...
>
> ehci_hcd 0000:00:02.1: USB 2.0 started, EHCI 1.00, driver 10 Dec 2004
> do_IRQ: cannot handle IRQ -1 vector 0x59 cpu 0
> ------------[ cut here ]------------
> Kernel BUG at 40206b11 [verbose debug info unavailable]
> invalid opcode: 0000 [#1] SMP
> Modules linked in:
>
> Pid: 70, comm: kasyncinit Not tainted (2.6.27-rc3-tip-00191-g98ccb89-dirty #23)
> EIP: 0060:[<40206b11>] EFLAGS: 00010092 CPU: 0
> EIP is at do_IRQ+0x6b/0xae
> EAX: 00000032 EBX: 00001d28 ECX: 00003434 EDX: 00000046
> ESI: 00000000 EDI: 00000059 EBP: c7a37d3c ESP: c7a37d14
>  DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
> Process kasyncinit (pid: 70, ti=c7a36000 task=c79c9860 task.ti=c7a36000)
> Stack: 40a74317 40814ea0 ffffffff 00000059 00000000 00000000 ffffffff c421bd20
>        c7a37d9c c7a37dac c7a37d7c 4020555f c421bd20 00000000 c421bd20 c7a37d9c
>        c7a37dac c7a37d7c 40b717f8 0000007b 0000007b 000000d8 ffffffa6 4080db6c
> Call Trace:
>  [<4020555f>] ? common_interrupt+0x23/0x28
>
>
> it is on 16cores system with 32bit bigsmp, so it is using phy_flat
> cpu 5 has apicid 9, and ioapic reg setting right with Dmod= 0 ( phys)
>
> but io_apic controller deliver that interrupt to cpu0 (with apicid =
> 4) instead of cpu 5 (with apic id = 9)
>
> look at the 64 bit, TARGET_CPUS for phys_flat is cpu_online_map
>
> and 32bit bigsmp TARGET_CPUS is only one cpu set and rotating with online cpu...
>
> Change 32bit bigsmp TARGE_CPUS ?

Set vector_allocation_domain to CPU_MASK_ALL on 32bit.  That doesn't give us
the benefit of per cpu vectors right now, but in my research there has not
been a 32bit kernel yet that has needed it.  We have never shared vectors
between 2 gsi on 32bit x86, we have only collapsed the irq space.

On x86_64 before I did the per cpu vectors there were machines that
combined multiple interrupt sources (gsi) into the same irq.  So
x86_64 has needed the per cpu vectors.

Which means in practice that the irq compression on x86_32 was just a hack to
with not having enough irq_desc entries.  I wish I had realized that last
time we were talking, as we could have unilaterally ripped out all of that
code as completely unnecessary on x86 and just bumped NR_IRQS to 1024 on
the boxes that had more than 256 gsis.

Eric

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