Re: [PATCH v4] kvm: Use a bitmap for tracking used GSIs

From: "Yang, Sheng" <sheng.yang@intel.com>
To: Alex Williamson <alex.williamson@hp.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"mst@redhat.com" <mst@redhat.com>
Subject: Re: [PATCH v4] kvm: Use a bitmap for tracking used GSIs
Date: Wed, 13 May 2009 12:58:43 +0800	[thread overview]
Message-ID: <200905131258.44935.sheng.yang@intel.com> (raw)
In-Reply-To: <20090513043835.6696.27384.stgit@dl380g6-3.ned.telco.ned.telco>

On Wednesday 13 May 2009 12:41:29 Alex Williamson wrote:
> We're currently using a counter to track the most recent GSI we've
> handed out.  This quickly hits KVM_MAX_IRQ_ROUTES when using device
> assignment with a driver that regularly toggles the MSI enable bit.
> This can mean only a few minutes of usable run time.  Instead, track
> used GSIs in a bitmap.
>
> Signed-off-by: Alex Williamson <alex.williamson@hp.com>
> ---

Acked.

-- 
regards
Yang, Sheng

>
>  v2: Added mutex to protect gsi bitmap
>  v3: Updated for comments from Michael Tsirkin
>      No longer depends on "[PATCH] kvm: device-assignment: Catch GSI
> overflow" v4: Fix gsi_bytes calculation noted by Sheng Yang
>
>  hw/device-assignment.c  |    4 ++
>  kvm/libkvm/kvm-common.h |    4 ++
>  kvm/libkvm/libkvm.c     |   81
> +++++++++++++++++++++++++++++++++++++++++------ kvm/libkvm/libkvm.h     |  
> 10 ++++++
>  4 files changed, 86 insertions(+), 13 deletions(-)
>
> diff --git a/hw/device-assignment.c b/hw/device-assignment.c
> index a7365c8..a6cc9b9 100644
> --- a/hw/device-assignment.c
> +++ b/hw/device-assignment.c
> @@ -561,8 +561,10 @@ static void free_dev_irq_entries(AssignedDevice *dev)
>  {
>      int i;
>
> -    for (i = 0; i < dev->irq_entries_nr; i++)
> +    for (i = 0; i < dev->irq_entries_nr; i++) {
>          kvm_del_routing_entry(kvm_context, &dev->entry[i]);
> +        kvm_free_irq_route_gsi(kvm_context, dev->entry[i].gsi);
> +    }
>      free(dev->entry);
>      dev->entry = NULL;
>      dev->irq_entries_nr = 0;
> diff --git a/kvm/libkvm/kvm-common.h b/kvm/libkvm/kvm-common.h
> index 591fb53..4b3cb51 100644
> --- a/kvm/libkvm/kvm-common.h
> +++ b/kvm/libkvm/kvm-common.h
> @@ -66,8 +66,10 @@ struct kvm_context {
>  #ifdef KVM_CAP_IRQ_ROUTING
>  	struct kvm_irq_routing *irq_routes;
>  	int nr_allocated_irq_routes;
> +	void *used_gsi_bitmap;
> +	int max_gsi;
> +	pthread_mutex_t gsi_mutex;
>  #endif
> -	int max_used_gsi;
>  };
>
>  int kvm_alloc_kernel_memory(kvm_context_t kvm, unsigned long memory,
> diff --git a/kvm/libkvm/libkvm.c b/kvm/libkvm/libkvm.c
> index ba0a5d1..3eaa120 100644
> --- a/kvm/libkvm/libkvm.c
> +++ b/kvm/libkvm/libkvm.c
> @@ -35,6 +35,7 @@
>  #include <errno.h>
>  #include <sys/ioctl.h>
>  #include <inttypes.h>
> +#include <pthread.h>
>  #include "libkvm.h"
>
>  #if defined(__x86_64__) || defined(__i386__)
> @@ -65,6 +66,8 @@
>  int kvm_abi = EXPECTED_KVM_API_VERSION;
>  int kvm_page_size;
>
> +static inline void set_bit(uint32_t *buf, unsigned int bit);
> +
>  struct slot_info {
>  	unsigned long phys_addr;
>  	unsigned long len;
> @@ -286,6 +289,9 @@ kvm_context_t kvm_init(struct kvm_callbacks *callbacks,
>  	int fd;
>  	kvm_context_t kvm;
>  	int r;
> +#ifdef KVM_CAP_IRQ_ROUTING
> +	int gsi_count, gsi_bytes, i;
> +#endif
>
>  	fd = open("/dev/kvm", O_RDWR);
>  	if (fd == -1) {
> @@ -322,6 +328,25 @@ kvm_context_t kvm_init(struct kvm_callbacks
> *callbacks, kvm->dirty_pages_log_all = 0;
>  	kvm->no_irqchip_creation = 0;
>  	kvm->no_pit_creation = 0;
> +#ifdef KVM_CAP_IRQ_ROUTING
> +	pthread_mutex_init(&kvm->gsi_mutex, NULL);
> +
> +	gsi_count = kvm_get_gsi_count(kvm);
> +	/* Round up so we can search ints using ffs */
> +	gsi_bytes = ((gsi_count + 31) / 32) * 4;
> +	kvm->used_gsi_bitmap = malloc(gsi_bytes);
> +	if (!kvm->used_gsi_bitmap)
> +		goto out_close;
> +	memset(kvm->used_gsi_bitmap, 0, gsi_bytes);
> +	kvm->max_gsi = gsi_bytes * 8;
> +
> +	/* Mark all the IOAPIC pin GSIs and any over-allocated
> +	 * GSIs as already in use. */
> +	for (i = 0; i < KVM_IOAPIC_NUM_PINS; i++)
> +		set_bit(kvm->used_gsi_bitmap, i);
> +	for (i = gsi_count; i < kvm->max_gsi; i++)
> +		set_bit(kvm->used_gsi_bitmap, i);
> +#endif
>
>  	return kvm;
>   out_close:
> @@ -1298,8 +1323,6 @@ int kvm_add_routing_entry(kvm_context_t kvm,
>  	new->flags = entry->flags;
>  	new->u = entry->u;
>
> -	if (entry->gsi > kvm->max_used_gsi)
> -		kvm->max_used_gsi = entry->gsi;
>  	return 0;
>  #else
>  	return -ENOSYS;
> @@ -1404,18 +1427,54 @@ int kvm_commit_irq_routes(kvm_context_t kvm)
>  #endif
>  }
>
> +#ifdef KVM_CAP_IRQ_ROUTING
> +static inline void set_bit(uint32_t *buf, unsigned int bit)
> +{
> +	buf[bit / 32] |= 1U << (bit % 32);
> +}
> +
> +static inline void clear_bit(uint32_t *buf, unsigned int bit)
> +{
> +	buf[bit / 32] &= ~(1U << (bit % 32));
> +}
> +
> +static int kvm_find_free_gsi(kvm_context_t kvm)
> +{
> +	int i, bit, gsi;
> +	uint32_t *buf = kvm->used_gsi_bitmap;
> +
> +	for (i = 0; i < kvm->max_gsi / 32; i++) {
> +		bit = ffs(~buf[i]);
> +		if (!bit)
> +			continue;
> +
> +		gsi = bit - 1 + i * 32;
> +		set_bit(buf, gsi);
> +		return gsi;
> +	}
> +
> +	return -ENOSPC;
> +}
> +#endif
> +
>  int kvm_get_irq_route_gsi(kvm_context_t kvm)
>  {
> +	int gsi = -ENOSYS;
> +
>  #ifdef KVM_CAP_IRQ_ROUTING
> -	if (kvm->max_used_gsi >= KVM_IOAPIC_NUM_PINS)  {
> -	    if (kvm->max_used_gsi <= kvm_get_gsi_count(kvm))
> -                return kvm->max_used_gsi + 1;
> -            else
> -                return -ENOSPC;
> -        } else
> -            return KVM_IOAPIC_NUM_PINS;
> -#else
> -	return -ENOSYS;
> +	pthread_mutex_lock(&kvm->gsi_mutex);
> +	gsi = kvm_find_free_gsi(kvm);
> +	pthread_mutex_unlock(&kvm->gsi_mutex);
> +#endif
> +	return gsi;
> +}
> +
> +void kvm_free_irq_route_gsi(kvm_context_t kvm, int gsi)
> +{
> +#ifdef KVM_CAP_IRQ_ROUTING
> +	pthread_mutex_lock(&kvm->gsi_mutex);
> +	clear_bit(kvm->used_gsi_bitmap, gsi);
> +	pthread_mutex_unlock(&kvm->gsi_mutex);
>  #endif
>  }
>
> diff --git a/kvm/libkvm/libkvm.h b/kvm/libkvm/libkvm.h
> index 4821a1e..845bb8a 100644
> --- a/kvm/libkvm/libkvm.h
> +++ b/kvm/libkvm/libkvm.h
> @@ -856,6 +856,16 @@ int kvm_commit_irq_routes(kvm_context_t kvm);
>   */
>  int kvm_get_irq_route_gsi(kvm_context_t kvm);
>
> +/*!
> + * \brief Free used GSI number
> + *
> + * Free used GSI number acquired from kvm_get_irq_route_gsi()
> + *
> + * \param kvm Pointer to the current kvm_context
> + * \param gsi GSI number to free
> + */
> +void kvm_free_irq_route_gsi(kvm_context_t kvm, int gsi);
> +
>  #ifdef KVM_CAP_DEVICE_MSIX
>  int kvm_assign_set_msix_nr(kvm_context_t kvm,
>  			   struct kvm_assigned_msix_nr *msix_nr);