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From: John Garry <john.garry@huawei.com>
To: Peng Zhang <zhangpeng.00@bytedance.com>,
	Ethan Zhao <haifeng.zhao@linux.intel.com>, <joro@8bytes.org>,
	<will@kernel.org>
Cc: <iommu@lists.linux.dev>, <linux-kernel@vger.kernel.org>,
	<robin.murphy@arm.com>
Subject: Re: [PATCH v2] iommu/iova: Optimize alloc_iova with rbtree_augmented
Date: Thu, 1 Sep 2022 11:45:58 +0100	[thread overview]
Message-ID: <1351998d-4fd7-dffb-c1fa-a0b1ca759123@huawei.com> (raw)
In-Reply-To: <4527c925-076b-a477-4ff8-697d75f16761@bytedance.com>

On 26/08/2022 11:28, Peng Zhang wrote:
> 
>> Though only 3-4 drivers use alloc_iova() directly, in my understanding
>>
>> your test has simulated the worst case, rcache doesn't work at all,
>>
>> "alloc_iova" +“remove_iova” number looks great for worst case.
> 
> There is another case, when the size to allocate greater to 2^5, even if 
> alloc_iova_fast() is used, alloc_iova() will always be called because 
> the maximum iova size that rcache supports to allocate is 32.
> IOVA_RANGE_CACHE_MAX_SIZE specifies the maximum size.
> 


If you really have a performance issue with alloc_iova_fast() -> 
alloc_iova() then I suggest that you consider trying to use 
dma_opt_mapping_size() to teach the DMA engine driver to not create 
requests whose overall size exceeds to the rcache limit.

Thanks,
John


  reply	other threads:[~2022-09-01 10:46 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-24  9:51 [PATCH v2] iommu/iova: Optimize alloc_iova with rbtree_augmented Peng Zhang
2022-08-24 12:30 ` Ethan Zhao
2022-08-25  8:10   ` [External] " Peng Zhang
2022-08-26  8:58     ` Ethan Zhao
2022-08-26 10:28       ` Peng Zhang
2022-09-01 10:45         ` John Garry [this message]
2022-09-02  3:30           ` Peng Zhang
2022-09-21  1:15 ` wangjie (L)
2022-09-21  3:55   ` Peng Zhang
2022-09-21 10:54     ` wangjie (L)

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