Re: PCI MSI issue for maxcpus=1
From: John Garry
Date: Mon Jan 17 2022 - 07:00:31 EST
On 17/01/2022 09:14, Marc Zyngier wrote:
I guess that for managed interrupts, it shouldn't matter, as these
interrupts should only be used when the relevant CPUs come online.
Would something like below help? Totally untested, as I don't have a
Multi-MSI capable device that I can plug in a GICv3 system (maybe I
should teach that to a virtio device...).
JFYI, NVMe PCI uses the same API (pci_alloc_irq_vectors_affinity()), but
does not suffer from this issue - for maxcpus=1 the driver looks to only
want 1x vector
Actually, if the CPU online status doesn't matter for managed affinity
interrupts, then the correct fix is this:
diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index d25b7a864bbb..af4e72a6be63 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -1624,7 +1624,7 @@ static int its_select_cpu(struct irq_data *d,
cpu = cpumask_pick_least_loaded(d, tmpmask);
} else {
- cpumask_and(tmpmask, irq_data_get_affinity_mask(d), cpu_online_mask);
+ cpumask_copy(tmpmask, irq_data_get_affinity_mask(d));
/* If we cannot cross sockets, limit the search to that node */
if ((its_dev->its->flags & ITS_FLAGS_WORKAROUND_CAVIUM_23144) &&
That produces a warn:
[ 7.833025] ------------[ cut here ]------------
[ 7.837634] WARNING: CPU: 0 PID: 44 at
drivers/irqchip/irq-gic-v3-its.c:298 valid_col+0x14/0x24
[ 7.846324] Modules linked in:
[ 7.849368] CPU: 0 PID: 44 Comm: kworker/0:3 Not tainted 5.16.0-dirty #119
[ 7.856230] Hardware name: Huawei D06 /D06, BIOS Hisilicon D06 UEFI RC0
- V1.16.01 03/15/2019
[ 7.864740] Workqueue: events work_for_cpu_fn
[ 7.869088] pstate: 804000c9 (Nzcv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 7.876037] pc : valid_col+0x14/0x24
[ 7.879600] lr : its_build_mapti_cmd+0x84/0x90
...
[ 7.961007] valid_col+0x14/0x24
[ 7.964223] its_send_single_command+0x4c/0x150
[ 7.968741] its_irq_domain_activate+0xc8/0x104
[ 7.973259] __irq_domain_activate_irq+0x5c/0xac
[ 7.977865] __irq_domain_activate_irq+0x38/0xac
[ 7.982471] irq_domain_activate_irq+0x3c/0x64
[ 7.986902] __msi_domain_alloc_irqs+0x1a8/0x2f4
[ 7.991507] msi_domain_alloc_irqs+0x20/0x2c
[ 7.995764] __pci_enable_msi_range+0x2ec/0x590
[ 8.000284] pci_alloc_irq_vectors_affinity+0xe0/0x140
[ 8.005410] hisi_sas_v3_probe+0x300/0xbe0
[ 8.009494] local_pci_probe+0x44/0xb0
[ 8.013232] work_for_cpu_fn+0x20/0x34
[ 8.016969] process_one_work+0x1d0/0x354
[ 8.020966] worker_thread+0x2c0/0x470
[ 8.024703] kthread+0x17c/0x190
[ 8.027920] ret_from_fork+0x10/0x20
[ 8.031485] ---[ end trace bb67cfc7eded7361 ]---
Apart from this, I assume that if another cpu comes online later in the
affinity mask I would figure that we want to target the irq to that cpu
(which I think we would not do here).
Cheers,
John