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

Paolo Bonzini
2013-07-03T10:58:14Z

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. */
>