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Message-ID: <1294176216.3636.38.camel@bwh-desktop>
Date: Tue, 04 Jan 2011 21:23:36 +0000
From: Ben Hutchings <bhutchings@...arflare.com>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
David Miller <davem@...emloft.net>,
Tom Herbert <therbert@...gle.com>,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
linux-net-drivers@...arflare.com
Subject: Re: [PATCH 2/2] lib: cpu_rmap: CPU affinity reverse-mapping
On Tue, 2011-01-04 at 22:17 +0100, Eric Dumazet wrote:
> Le mardi 04 janvier 2011 à 19:39 +0000, Ben Hutchings a écrit :
> > When initiating I/O on a multiqueue and multi-IRQ device, we may want
> > to select a queue for which the response will be handled on the same
> > or a nearby CPU. This requires a reverse-map of IRQ affinity. Add
> > library functions to support a generic reverse-mapping from CPUs to
> > objects with affinity and the specific case where the objects are
> > IRQs.
[...]
> > +/**
> > + * struct cpu_rmap - CPU affinity reverse-map
> > + * @near: For each CPU, the index and distance to the nearest object,
> > + * based on affinity masks
> > + * @size: Number of objects to be reverse-mapped
> > + * @used: Number of objects added
> > + * @obj: Array of object pointers
> > + */
> > +struct cpu_rmap {
> > + struct {
> > + u16 index;
> > + u16 dist;
> > + } near[NR_CPUS];
>
> This [NR_CPUS] is highly suspect.
>
> Are you sure you cant use a per_cpu allocation here ?
I think that would be a waste of space in shared caches, as this is
read-mostly.
> > + u16 size, used;
> > + void *obj[0];
> > +};
> > +#define CPU_RMAP_DIST_INF 0xffff
> > +
>
>
> > +
> > +/**
> > + * alloc_cpu_rmap - allocate CPU affinity reverse-map
> > + * @size: Number of objects to be mapped
> > + * @flags: Allocation flags e.g. %GFP_KERNEL
> > + */
>
> I really doubt you need other than GFP_KERNEL. (Especially if you switch
> to per_cpu alloc ;) )
[...]
I agree, but this is consistent with ~all other allocation functions.
Ben.
--
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.
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