linux-kernel - Re: [PATCH 04/10] dmapool: improve accuracy of debug statistics

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Message-ID: <a57d3dde-ac45-be9c-5c16-263415060334@cybernetics.com>
Date:   Tue, 31 May 2022 15:52:40 -0400
From:   Tony Battersby <tonyb@...ernetics.com>
To:     Robin Murphy <robin.murphy@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     iommu@...ts.linux-foundation.org, kernel-team@...com,
        Matthew Wilcox <willy@...radead.org>,
        Keith Busch <kbusch@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH 04/10] dmapool: improve accuracy of debug statistics

On 5/31/22 15:48, Robin Murphy wrote:
> On 2022-05-31 19:17, Tony Battersby wrote:
>
>>   				 pool->name, blocks,
>> -				 (size_t) pages *
>> -				 (pool->allocation / pool->size),
>> +				 (size_t) pages * pool->blks_per_alloc,
>>   				 pool->size, pages);
>>   		size -= temp;
>>   		next += temp;
>> @@ -168,6 +168,9 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
>>   	retval->size = size;
>>   	retval->boundary = boundary;
>>   	retval->allocation = allocation;
>> +	retval->blks_per_alloc =
>> +		(allocation / boundary) * (boundary / size) +
>> +		(allocation % boundary) / size;
> Do we really need to store this? Sure, 4 divisions (which could possibly 
> be fewer given the constraints on boundary) isn't the absolute cheapest 
> calculation, but I still can't imagine anyone would be polling sysfs 
> stats hard enough to even notice.
>
The stored value is also used in patch #5, in more performance-critical
code, although only when debug is enabled.

Tony