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Date: Mon, 20 May 2013 13:57:06 -0400
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Zhenzhong Duan <zhenzhong.duan@oracle.com>,
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        Feng Jin <joe.jin@oracle.com>, Chien Yen <chien.yen@oracle.com>
Subject: Re: [PATCH] xen: reuse the same pirq allocated when driver load
 first time
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> > Hi Stefano,
> > 
> > do you work out a patch for me to test?
> 
> I'll be traveling/busy for a few weeks, maybe it's best if someone else
> picks up this work item.

This little test-case below should have worked:

#include <linux/module.h>
#include <linux/kthread.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <xen/xen.h>
#include <xen/page.h>
#include <asm/xen/hypervisor.h>
#include <xen/features.h>
#include <xen/events.h>

MODULE_AUTHOR("Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>");
MODULE_DESCRIPTION("alloc_and_unmap");
MODULE_LICENSE("GPL");
MODULE_VERSION("0.1");

static int do_it(void)
{
	struct physdev_get_free_pirq op_get_free_pirq;
	struct physdev_unmap_pirq unmap_irq;
	int rc, pirq;

	op_get_free_pirq.type = MAP_PIRQ_TYPE_MSI;
 	rc = HYPERVISOR_physdev_op(PHYSDEVOP_get_free_pirq, &op_get_free_pirq);
	if (rc) {
		printk(KERN_WARNING "%s:%d rc:%d\n", __func__, __LINE__, rc);
		return rc;
	}
	pirq = op_get_free_pirq.pirq;
	unmap_irq.pirq = pirq;
	unmap_irq.domid = DOMID_SELF;
	rc = HYPERVISOR_physdev_op(PHYSDEVOP_unmap_pirq, &unmap_irq);
	if (rc) {
		printk(KERN_WARNING "unmap irq failed %d\n", rc);
		return rc;
	}
	printk("PIRQ: %d\n", pirq);
	return 0;
}
static int __init alloc_and_unmap_init(void)
{
	int i;

	for (i = 0; i < 10; i++)
		if (do_it())
			break;
	return 0;
}
static void __exit alloc_and_unmap_exit(void)
{
}
module_init(alloc_and_unmap_init);
module_exit(alloc_and_unmap_exit);


But I get:

# insmod /alloc_and_unmap.ko 
[   34.899277] PIRQ: 55
[   34.901846] PIRQ: 54
[   34.904351] PIRQ: 53
[   34.906921] PIRQ: 52
[   34.909451] PIRQ: 51
[   34.912038] PIRQ: 50
[   34.914650] PIRQ: 49
[   34.917205] PIRQ: 48
[   34.919776] PIRQ: 47
[   34.922339] PIRQ: 46

Which means there is some bug in the hypervisor as well (This is with Xen 4.3
and traditional QEMU - not that it matters as I am just doing these hypercalls).


At this point I think that upstream option is to save the PIRQ value and re-use it.
Will post a patch for it.