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Message-ID: <YrL02y/fYxDkDRlA@infradead.org>
Date: Wed, 22 Jun 2022 03:54:19 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Tianyu Lan <ltykernel@...il.com>
Cc: corbet@....net, hch@...radead.org, m.szyprowski@...sung.com,
robin.murphy@....com, paulmck@...nel.org,
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songmuchun@...edance.com, rdunlap@...radead.org,
damien.lemoal@...nsource.wdc.com, michael.h.kelley@...rosoft.com,
kys@...rosoft.com, Tianyu Lan <Tianyu.Lan@...rosoft.com>,
iommu@...ts.linux-foundation.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, vkuznets@...hat.com,
wei.liu@...nel.org, parri.andrea@...il.com,
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kirill.shutemov@...el.com, andi.kleen@...el.com,
Andi Kleen <ak@...ux.intel.com>
Subject: Re: [RFC PATCH V4 1/1] swiotlb: Split up single swiotlb lock
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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