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From: Will Deacon <will@kernel.org>
To: John Garry <john.garry@huawei.com>
Cc: joro@8bytes.org, robin.murphy@arm.com, baolu.lu@linux.intel.com,
	iommu@lists.linux-foundation.org, linuxarm@huawei.com,
	thierry.reding@gmail.com, airlied@linux.ie, daniel@ffwll.ch,
	jonathanh@nvidia.com, sakari.ailus@linux.intel.com,
	bingbu.cao@intel.com, tian.shu.qiu@intel.com, mchehab@kernel.org,
	gregkh@linuxfoundation.org, digetx@gmail.com, mst@redhat.com,
	jasowang@redhat.com, linux-kernel@vger.kernel.org,
	chenxiang66@hisilicon.com
Subject: Re: [PATCH v4 2/6] iova: Allow rcache range upper limit to be flexible
Date: Mon, 2 Aug 2021 16:01:53 +0100	[thread overview]
Message-ID: <20210802150153.GC28735@willie-the-truck> (raw)
In-Reply-To: <1626259003-201303-3-git-send-email-john.garry@huawei.com>

On Wed, Jul 14, 2021 at 06:36:39PM +0800, John Garry wrote:
> Some LLDs may request DMA mappings whose IOVA length exceeds that of the
> current rcache upper limit.

What's an LLD?

> This means that allocations for those IOVAs will never be cached, and
> always must be allocated and freed from the RB tree per DMA mapping cycle.
> This has a significant effect on performance, more so since commit
> 4e89dce72521 ("iommu/iova: Retry from last rb tree node if iova search
> fails"), as discussed at [0].
> 
> As a first step towards allowing the rcache range upper limit be
> configured, hold this value in the IOVA rcache structure, and allocate
> the rcaches separately.
> 
> [0] https://lore.kernel.org/linux-iommu/20210129092120.1482-1-thunder.leizhen@huawei.com/
> 
> Signed-off-by: John Garry <john.garry@huawei.com>
> ---
>  drivers/iommu/dma-iommu.c |  2 +-
>  drivers/iommu/iova.c      | 23 +++++++++++++++++------
>  include/linux/iova.h      |  4 ++--
>  3 files changed, 20 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 98ba927aee1a..4772278aa5da 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -434,7 +434,7 @@ static dma_addr_t iommu_dma_alloc_iova(struct iommu_domain *domain,
>  	 * rounding up anything cacheable to make sure that can't happen. The
>  	 * order of the unadjusted size will still match upon freeing.
>  	 */
> -	if (iova_len < (1 << (IOVA_RANGE_CACHE_MAX_SIZE - 1)))
> +	if (iova_len < (1 << (iovad->rcache_max_size - 1)))
>  		iova_len = roundup_pow_of_two(iova_len);
>  
>  	dma_limit = min_not_zero(dma_limit, dev->bus_dma_limit);
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index b6cf5f16123b..07ce73fdd8c1 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -15,6 +15,8 @@
>  /* The anchor node sits above the top of the usable address space */
>  #define IOVA_ANCHOR	~0UL
>  
> +#define IOVA_RANGE_CACHE_MAX_SIZE 6    /* log of max cached IOVA range size (in pages) */

Is that the same as an 'order'? i.e. IOVA_RANGE_CACHE_MAX_ORDER?

> +
>  static bool iova_rcache_insert(struct iova_domain *iovad,
>  			       unsigned long pfn,
>  			       unsigned long size);
> @@ -881,7 +883,14 @@ static void init_iova_rcaches(struct iova_domain *iovad)
>  	unsigned int cpu;
>  	int i;
>  
> -	for (i = 0; i < IOVA_RANGE_CACHE_MAX_SIZE; ++i) {
> +	iovad->rcache_max_size = IOVA_RANGE_CACHE_MAX_SIZE;
> +
> +	iovad->rcaches = kcalloc(iovad->rcache_max_size,
> +				 sizeof(*iovad->rcaches), GFP_KERNEL);
> +	if (!iovad->rcaches)
> +		return;

Returning quietly here doesn't seem like the right thing to do. At least, I
don't think the rest of the functions here are checking rcaches against
NULL.

Will

  reply	other threads:[~2021-08-02 15:02 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-14 10:36 [PATCH v4 0/6] iommu: Allow IOVA rcache range be configured John Garry
2021-07-14 10:36 ` [PATCH v4 1/6] iommu: Refactor iommu_group_store_type() John Garry
2021-08-02 14:46   ` Will Deacon
2021-07-14 10:36 ` [PATCH v4 2/6] iova: Allow rcache range upper limit to be flexible John Garry
2021-08-02 15:01   ` Will Deacon [this message]
2021-08-02 15:23     ` John Garry
2021-08-02 16:09       ` Robin Murphy
2021-07-14 10:36 ` [PATCH v4 3/6] iommu: Allow iommu_change_dev_def_domain() realloc default domain for same type John Garry
2021-07-14 10:36 ` [PATCH v4 4/6] iommu: Allow max opt DMA len be set for a group via sysfs John Garry
2021-07-14 10:36 ` [PATCH v4 5/6] iova: Add iova_len argument to init_iova_domain() John Garry
2021-08-02 15:06   ` Will Deacon
2021-08-02 16:06     ` John Garry
2021-08-02 16:16       ` Robin Murphy
2021-08-02 16:40         ` John Garry
2021-08-02 17:18           ` John Garry
2021-09-21  8:48         ` John Garry
2021-07-14 10:36 ` [PATCH v4 6/6] dma-iommu: Pass iova len for IOVA domain init John Garry

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