Re: [PATCH] iommu/iova: Update cached node pointer when current node fails to get any free IOVA

[Ganapatrao Kulkarni <gklkml16@gmail.com>]

Hi Robin,


On Mon, Jul 30, 2018 at 12:40 PM, Ganapatrao Kulkarni
<gklkml16@gmail.com> wrote:
> On Fri, Jul 27, 2018 at 9:48 PM, Robin Murphy <robin.murphy@arm.com> wrote:
>> On 27/07/18 13:56, Ganapatrao Kulkarni wrote:
>> [...]
>>>>>
>>>>> did you get any chance to look in to this issue?
>>>>> i am waiting for your suggestion/patch for this issue!
>>>>
>>>>
>>>>
>>>> I got as far as [1], but I wasn't sure how much I liked it, since it
>>>> still
>>>> seems a little invasive for such a specific case (plus I can't remember
>>>> if
>>>> it's actually been debugged or not). I think in the end I started
>>>> wondering
>>>> whether it's even worth bothering with the 32-bit optimisation for PCIe
>>>> devices - 4 extra bytes worth of TLP is surely a lot less significant
>>>> than
>>>> every transaction taking up to 50% more bus cycles was for legacy PCI.
>>>
>>>
>>> how about tracking previous attempt to get 32bit range iova and avoid
>>> further attempts, if it was failed. Later Resume attempts once
>>> replenish happens.
>>> Created patch for the same [2]
>>
>>
>> Ooh, that's a much neater implementation of essentially the same concept -
>> now why couldn't I think of that? :)
>>
>> Looks like it should be possible to make it entirely self-contained too,
>> since alloc_iova() is in a position to both test and update the flag based
>> on the limit_pfn passed in.
>
> is below patch much better?

testing with this diff looks ok, shall i send formal patch with your Acked-by?
>
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index 83fe262..abb15d6 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -56,6 +56,7 @@ init_iova_domain(struct iova_domain *iovad, unsigned
> long granule,
>      iovad->granule = granule;
>      iovad->start_pfn = start_pfn;
>      iovad->dma_32bit_pfn = 1UL << (32 - iova_shift(iovad));
> +    iovad->free_32bit_pfns = true;
>      iovad->flush_cb = NULL;
>      iovad->fq = NULL;
>      iovad->anchor.pfn_lo = iovad->anchor.pfn_hi = IOVA_ANCHOR;
> @@ -139,8 +140,10 @@ __cached_rbnode_delete_update(struct iova_domain
> *iovad, struct iova *free)
>
>      cached_iova = rb_entry(iovad->cached32_node, struct iova, node);
>      if (free->pfn_hi < iovad->dma_32bit_pfn &&
> -        free->pfn_lo >= cached_iova->pfn_lo)
> +        free->pfn_lo >= cached_iova->pfn_lo) {
>          iovad->cached32_node = rb_next(&free->node);
> +        iovad->free_32bit_pfns = true;
> +    }
>
>      cached_iova = rb_entry(iovad->cached_node, struct iova, node);
>      if (free->pfn_lo >= cached_iova->pfn_lo)
> @@ -290,6 +293,10 @@ alloc_iova(struct iova_domain *iovad, unsigned long size,
>      struct iova *new_iova;
>      int ret;
>
> +    if (limit_pfn < iovad->dma_32bit_pfn &&
> +            !iovad->free_32bit_pfns)
> +        return NULL;
> +
>      new_iova = alloc_iova_mem();
>      if (!new_iova)
>          return NULL;
> @@ -299,6 +306,8 @@ alloc_iova(struct iova_domain *iovad, unsigned long size,
>
>      if (ret) {
>          free_iova_mem(new_iova);
> +        if (limit_pfn < iovad->dma_32bit_pfn)
> +            iovad->free_32bit_pfns = false;
>          return NULL;
>      }
>
> diff --git a/include/linux/iova.h b/include/linux/iova.h
> index 928442d..3810ba9 100644
> --- a/include/linux/iova.h
> +++ b/include/linux/iova.h
> @@ -96,6 +96,7 @@ struct iova_domain {
>                             flush-queues */
>      atomic_t fq_timer_on;            /* 1 when timer is active, 0
>                             when not */
> +    bool    free_32bit_pfns;
>  };
>
>  static inline unsigned long iova_size(struct iova *iova)
> --
> 2.9.4
>>
>> Robin.
>>
>>
>>>
>>> [2]
>>> https://github.com/gpkulkarni/linux/commit/e2343a3e1f55cdeb5694103dd354bcb881dc65c3
>>> note, the testing of this patch is in progress.
>>>
>>>>
>>>> Robin.
>>>>
>>>> [1]
>>>>
>>>> http://www.linux-arm.org/git?p=linux-rm.git;a=commitdiff;h=a8e0e4af10ebebb3669750e05bf0028e5bd6afe8
>>>
>>>
>>> thanks
>>> Ganapat
>>>
>>
>
> thanks
> Ganapat

thanks
Ganapat