Re: [PATCH 1/1] Revert "iommu/iova: Retry from last rb tree node if iova search fails"

["chenxiang (M)" <chenxiang66@hisilicon.com>]

Hi Robin,


在 2021/1/29 20:03, Robin Murphy 写道:
> On 2021-01-29 09:48, Leizhen (ThunderTown) wrote:
>>
>> Currently, we are thinking about the solution to the problem. 
>> However, because the end time of v5.11 is approaching, this patch is 
>> sent first.
>
> However, that commit was made for a reason - how do we justify that 
> one thing being slow is more important than another thing being 
> completely broken? It's not practical to just keep doing the patch 
> hokey-cokey based on whoever shouts loudest :(
>
>> On 2021/1/29 17:21, Zhen Lei wrote:
>>> This reverts commit 4e89dce725213d3d0b0475211b500eda4ef4bf2f.
>>>
>>> We find that this patch has a great impact on performance. According to
>>> our test: the iops decreases from 1655.6K to 893.5K, about half.
>>>
>>> Hardware: 1 SAS expander with 12 SAS SSD
>>> Command:  Only the main parameters are listed.
>>>            fio bs=4k rw=read iodepth=128 cpus_allowed=0-127
>
> FWIW, I'm 99% sure that what you really want is [1], but then you get 
> to battle against an unknown quantity of dodgy firmware instead.
>
> Robin.
>
> [1] 
> https://lore.kernel.org/linux-iommu/d412c292d222eb36469effd338e985f9d9e24cd6.1594207679.git.robin.murphy@arm.com/

Thank you for pointing that out. I have tested it, and it solves the 
performance drop issue mentioned above.
I noticed that you sent it July 2020, and do you have a plan to merge it 
recently?


>
>>> Fixes: 4e89dce72521 ("iommu/iova: Retry from last rb tree node if 
>>> iova search fails")
>>> Tested-by: Xiang Chen <chenxiang66@hisilicon.com>
>>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>>> ---
>>>   drivers/iommu/iova.c | 23 ++++++-----------------
>>>   1 file changed, 6 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
>>> index d20b8b333d30d17..f840c7207efbced 100644
>>> --- a/drivers/iommu/iova.c
>>> +++ b/drivers/iommu/iova.c
>>> @@ -185,9 +185,8 @@ static int __alloc_and_insert_iova_range(struct 
>>> iova_domain *iovad,
>>>       struct rb_node *curr, *prev;
>>>       struct iova *curr_iova;
>>>       unsigned long flags;
>>> -    unsigned long new_pfn, retry_pfn;
>>> +    unsigned long new_pfn;
>>>       unsigned long align_mask = ~0UL;
>>> -    unsigned long high_pfn = limit_pfn, low_pfn = iovad->start_pfn;
>>>         if (size_aligned)
>>>           align_mask <<= fls_long(size - 1);
>>> @@ -200,25 +199,15 @@ static int 
>>> __alloc_and_insert_iova_range(struct iova_domain *iovad,
>>>         curr = __get_cached_rbnode(iovad, limit_pfn);
>>>       curr_iova = rb_entry(curr, struct iova, node);
>>> -    retry_pfn = curr_iova->pfn_hi + 1;
>>> -
>>> -retry:
>>>       do {
>>> -        high_pfn = min(high_pfn, curr_iova->pfn_lo);
>>> -        new_pfn = (high_pfn - size) & align_mask;
>>> +        limit_pfn = min(limit_pfn, curr_iova->pfn_lo);
>>> +        new_pfn = (limit_pfn - size) & align_mask;
>>>           prev = curr;
>>>           curr = rb_prev(curr);
>>>           curr_iova = rb_entry(curr, struct iova, node);
>>> -    } while (curr && new_pfn <= curr_iova->pfn_hi && new_pfn >= 
>>> low_pfn);
>>> -
>>> -    if (high_pfn < size || new_pfn < low_pfn) {
>>> -        if (low_pfn == iovad->start_pfn && retry_pfn < limit_pfn) {
>>> -            high_pfn = limit_pfn;
>>> -            low_pfn = retry_pfn;
>>> -            curr = &iovad->anchor.node;
>>> -            curr_iova = rb_entry(curr, struct iova, node);
>>> -            goto retry;
>>> -        }
>>> +    } while (curr && new_pfn <= curr_iova->pfn_hi);
>>> +
>>> +    if (limit_pfn < size || new_pfn < iovad->start_pfn) {
>>>           iovad->max32_alloc_size = size;
>>>           goto iova32_full;
>>>       }
>>>
>>
>
> .
>


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