Re: [RFC PATCH V4 1/1] swiotlb: Split up single swiotlb lock

From: Dongli Zhang <dongli.zhang@oracle.com>
To: Christoph Hellwig <hch@infradead.org>, Tianyu Lan <ltykernel@gmail.com>
Cc: linux-hyperv@vger.kernel.org, linux-doc@vger.kernel.org,
	kys@microsoft.com, wei.liu@kernel.org,
	Andi Kleen <ak@linux.intel.com>,
	corbet@lwn.net, damien.lemoal@opensource.wdc.com,
	michael.h.kelley@microsoft.com, andi.kleen@intel.com, bp@suse.de,
	parri.andrea@gmail.com, thomas.lendacky@amd.com,
	Tianyu Lan <Tianyu.Lan@microsoft.com>,
	paulmck@kernel.org, kirill.shutemov@intel.com,
	songmuchun@bytedance.com, tglx@linutronix.de,
	akpm@linux-foundation.org, rdunlap@infradead.org,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	vkuznets@redhat.com, robin.murphy@arm.com
Subject: Re: [RFC PATCH V4 1/1] swiotlb: Split up single swiotlb lock
Date: Wed, 22 Jun 2022 05:55:46 -0700	[thread overview]
Message-ID: <09751b9b-0912-d2f2-5636-cde6db6afaa3@oracle.com> (raw)
In-Reply-To: <YrL02y/fYxDkDRlA@infradead.org>

I will build the next RFC version of 64-bit swiotlb on top of this patch (or
next version of this patch), so that it will render a more finalized view of
32-bt/64-bit plus multiple area.

Thank you very much!

Dongli Zhang

On 6/22/22 3:54 AM, Christoph Hellwig wrote:
> Thanks,
> 
> this looks pretty good to me.  A few comments below:
> 
> On Fri, Jun 17, 2022 at 10:47:41AM -0400, Tianyu Lan wrote:
>> +/**
>> + * struct io_tlb_area - IO TLB memory area descriptor
>> + *
>> + * This is a single area with a single lock.
>> + *
>> + * @used:	The number of used IO TLB block.
>> + * @index:	The slot index to start searching in this area for next round.
>> + * @lock:	The lock to protect the above data structures in the map and
>> + *		unmap calls.
>> + */
>> +struct io_tlb_area {
>> +	unsigned long used;
>> +	unsigned int index;
>> +	spinlock_t lock;
>> +};
> 
> This can go into swiotlb.c.
> 
>> +void __init swiotlb_adjust_nareas(unsigned int nareas);
> 
> And this should be marked static.
> 
>> +#define DEFAULT_NUM_AREAS 1
> 
> I'd drop this define, the magic 1 and a > 1 comparism seems to
> convey how it is used much better as the checks aren't about default
> or not, but about larger than one.
> 
> I also think that we want some good way to size the default, e.g.
> by number of CPUs or memory size.
> 
>> +void __init swiotlb_adjust_nareas(unsigned int nareas)
>> +{
>> +	if (!is_power_of_2(nareas)) {
>> +		pr_err("swiotlb: Invalid areas parameter %d.\n", nareas);
>> +		return;
>> +	}
>> +
>> +	default_nareas = nareas;
>> +
>> +	pr_info("area num %d.\n", nareas);
>> +	/* Round up number of slabs to the next power of 2.
>> +	 * The last area is going be smaller than the rest if
>> +	 * default_nslabs is not power of two.
>> +	 */
> 
> Please follow the normal kernel comment style with a /* on its own line.
> 
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