Re: [PATCH 1/2] KVM: kvm-io: support cookies

[Paolo Bonzini <pbonzini@redhat.com>]

Il 03/07/2013 12:51, Cornelia Huck ha scritto:
> On Wed, 03 Jul 2013 11:21:23 +0200
> Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
>> Il 03/07/2013 11:05, Paolo Bonzini ha scritto:
>>> Nice idea, though I don't really like the duplication between
>>> kvm_io_bus_write and kvm_io_bus_write_cookie.
>>>
>>> Can you make kvm_io_bus_write, and perhaps kvm_io_bus_read too, return
>>> the cookie, and return -EINVAL here if the cookie is garbage?
>>
>> On second though---no need to return -EINVAL, you can just pass the
>> cookie by value and tail-call kvm_io_bus_write.  Whatever makes the s390
>> code look nicer.
> 
> It would probably be easier to have the non-cookie functions call the
> cookie functions with a negative cookie value, like the following
> (untested):

That would work too, but it adds a small overhead to the non-cookie
calls.  If Gleb agrees with you, it is fine; otherwise, I'd prefer that
one explicitly requests the cookie on input.

Paolo

> From 12a6e9821f1a07ecd918e927a4049263ad6f1724 Mon Sep 17 00:00:00 2001
> From: Cornelia Huck <cornelia.huck@de.ibm.com>
> Date: Tue, 2 Jul 2013 13:30:56 +0200
> Subject: [PATCH] KVM: kvm-io: support cookies
> 
> Add new functions kvm_io_bus_{read,write}_cookie() that allows users of
> the kvm io infrastructure to use a cookie value to speed up lookup of a
> device on an io bus.
> 
> Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> ---
>  include/linux/kvm_host.h |  4 +++
>  virt/kvm/kvm_main.c      | 82 ++++++++++++++++++++++++++++++++++++++----------
>  2 files changed, 70 insertions(+), 16 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index e3aae6d..97849fc 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -159,8 +159,12 @@ enum kvm_bus {
>  
>  int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
>  		     int len, const void *val);
> +int kvm_io_bus_write_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> +			    int len, const void *val, long *cookie);
>  int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr, int len,
>  		    void *val);
> +int kvm_io_bus_read_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> +			   int len, void *val, long *cookie);
>  int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
>  			    int len, struct kvm_io_device *dev);
>  int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 1580dd4..21e6d7d 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2863,11 +2863,11 @@ static int kvm_io_bus_get_first_dev(struct kvm_io_bus *bus,
>  	return off;
>  }
>  
> -/* kvm_io_bus_write - called under kvm->slots_lock */
> -int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> -		     int len, const void *val)
> +/* kvm_io_bus_write_cookie - called under kvm->slots_lock */
> +int kvm_io_bus_write_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> +			    int len, const void *val, long *cookie)
>  {
> -	int idx;
> +	int idx, ret = -EOPNOTSUPP;
>  	struct kvm_io_bus *bus;
>  	struct kvm_io_range range;
>  
> @@ -2877,25 +2877,50 @@ int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
>  	};
>  
>  	bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
> +
> +	/* First try the device referenced by *cookie. */
> +	if ((*cookie >= 0) && (*cookie < bus->dev_count) &&
> +	    (kvm_io_bus_sort_cmp(&range, &bus->range[*cookie]) == 0))
> +		if (!kvm_iodevice_write(bus->range[*cookie].dev, addr, len,
> +					val))
> +			return 0;
> +
> +	/*
> +	 * *cookie contained garbage; fall back to search and return the
> +	 * correct value in *cookie.
> +	 */
>  	idx = kvm_io_bus_get_first_dev(bus, addr, len);
>  	if (idx < 0)
> -		return -EOPNOTSUPP;
> +		goto out;
>  
>  	while (idx < bus->dev_count &&
>  		kvm_io_bus_sort_cmp(&range, &bus->range[idx]) == 0) {
> -		if (!kvm_iodevice_write(bus->range[idx].dev, addr, len, val))
> -			return 0;
> +		if (!kvm_iodevice_write(bus->range[idx].dev, addr, len, val)) {
> +			ret = 0;
> +			goto out;
> +		}
>  		idx++;
>  	}
> +	idx = -ENOENT;
> +out:
> +	*cookie = idx;
> +	return ret;
> +}
> +
> +/* kvm_io_bus_write - called under kvm->slots_lock */
> +int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> +		     int len, const void *val)
> +{
> +	long tmp = -1;
>  
> -	return -EOPNOTSUPP;
> +	return kvm_io_bus_write_cookie(kvm, bus_idx, addr, len, val, &tmp);
>  }
>  
> -/* kvm_io_bus_read - called under kvm->slots_lock */
> -int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> -		    int len, void *val)
> +/* kvm_io_bus_read_cookie - called under kvm->slots_lock */
> +int kvm_io_bus_read_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> +			   int len, void *val, long *cookie)
>  {
> -	int idx;
> +	int idx, ret = -EOPNOTSUPP;
>  	struct kvm_io_bus *bus;
>  	struct kvm_io_range range;
>  
> @@ -2905,18 +2930,43 @@ int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
>  	};
>  
>  	bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
> +
> +	/* First try the device referenced by *cookie. */
> +	if ((*cookie >= 0) && (*cookie < bus->dev_count) &&
> +	    (kvm_io_bus_sort_cmp(&range, &bus->range[*cookie]) == 0))
> +		if (!kvm_iodevice_read(bus->range[*cookie].dev, addr, len,
> +				       val))
> +			return 0;
> +
> +	/*
> +	 * *cookie contained garbage; fall back to search and return the
> +	 * correct value in *cookie.
> +	 */
>  	idx = kvm_io_bus_get_first_dev(bus, addr, len);
>  	if (idx < 0)
> -		return -EOPNOTSUPP;
> +		goto out;
>  
>  	while (idx < bus->dev_count &&
>  		kvm_io_bus_sort_cmp(&range, &bus->range[idx]) == 0) {
> -		if (!kvm_iodevice_read(bus->range[idx].dev, addr, len, val))
> -			return 0;
> +		if (!kvm_iodevice_read(bus->range[idx].dev, addr, len, val)) {
> +			ret = 0;
> +			goto out;
> +		}
>  		idx++;
>  	}
> +	idx = -ENOENT;
> +out:
> +	*cookie = idx;
> +	return ret;
> +}
> +
> +/* kvm_io_bus_read - called under kvm->slots_lock */
> +int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> +		    int len, void *val)
> +{
> +	long tmp = -1;
>  
> -	return -EOPNOTSUPP;
> +	return kvm_io_bus_read_cookie(kvm, bus_idx, addr, len, val, &tmp);
>  }
>  
>  /* Caller must hold slots_lock. */
>